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❓Fresh grapes contain 90% water by weight, while dried grapes contain 20% water by weight. The weight of dry grapes available from a certain amount of fresh grapes is 3.75 kg. What is the weight of the fresh grapes?
💡To determine the weight of the fresh grapes, we start by noting the water content percentages and the weight of the dried grapes.1. **Fresh Grapes:** - Water Content: 90% - Non-Water Content: 10%2. **Dried Grapes:** - Water Content: 20% - Non-Water Content: 80% - Weight of Dried Grapes: 3.75 kgSince the non-water content remains constant during the drying process, we can set up the equation:10% of Fresh Grapes = 80% of Dried GrapesMathematically, this is:0.10 * F = 0.80 * 3.75Solving for F:F = (0.80 * 3.75) / 0.10F = 3 / 0.10F = 30 kgTherefore, the weight of the fresh grapes is 30 kg.
❓On Monday, Sydney sends some texts each to Allison and Brittney. On Tuesday, she sends 15 texts to each of them. In total, Sydney sent 40 texts to Allison and Brittney on both days. How many texts did Sydney send to each of them on Monday?
💡First, I need to determine how many texts Sydney sent to Allison and Brittney on Monday. I'll start by defining variables for the unknown quantities. Let ( A ) represent the number of texts sent to Allison on Monday, and ( B ) represent the number of texts sent to Brittney on Monday.According to the problem, on Tuesday, Sydney sent 15 texts to each of them. So, on Tuesday, she sent 15 texts to Allison and 15 texts to Brittney.The total number of texts sent to both Allison and Brittney over both days is 40. This includes the texts sent on Monday and Tuesday. I can write this as an equation:[A + B + 15 + 15 = 40]Combining the constant terms (the texts sent on Tuesday), I get:[A + B + 30 = 40]Now, I'll subtract 30 from both sides to solve for ( A + B ):[A + B = 40 - 30][A + B = 10]So, Sydney sent a total of 10 texts on Monday to both Allison and Brittney. Since there's no additional information differentiating the number of texts sent to each person on Monday, I can only conclude that the sum of texts sent to both of them on Monday is 10. If I need to know exactly how many texts were sent to each person on Monday, I would need more information.
❓The library is divided into different sections for different types of books. The science fiction section has 8 books. If each book has a certain number of pages, in total all the books have 3824 pages. How many pages does each book have?
💡Okay, so I've got this problem about the library's science fiction section. It says there are 8 books, and together, all these books have a total of 3,824 pages. The question is asking how many pages each book has. Hmm, that sounds like I need to find out the average number of pages per book.Alright, let's break this down. If there are 8 books and together they have 3,824 pages, then to find out how many pages each book has on average, I should probably divide the total number of pages by the number of books. That makes sense because if I spread out the total pages equally among all the books, that should give me the average number of pages per book.So, mathematically, that would be:Number of pages per book = Total pages / Number of booksPlugging in the numbers:Number of pages per book = 3,824 / 8Okay, now I need to do this division. Let me see, 3,824 divided by 8. I think I can do this step by step.First, let's see how many times 8 goes into 38. Well, 8 times 4 is 32, and 8 times 5 is 40, which is too big. So, 4 times 8 is 32. Subtracting that from 38 gives me 6.Now, bring down the next digit, which is 2, making it 62. How many times does 8 go into 62? Let's see, 8 times 7 is 56, and 8 times 8 is 64, which is too big. So, 7 times 8 is 56. Subtracting that from 62 gives me 6.Bring down the next digit, which is 4, making it 64. How many times does 8 go into 64? Exactly 8 times. So, 8 times 8 is 64, and subtracting that leaves me with 0.So, putting it all together, 3,824 divided by 8 is 478. That means each book has 478 pages on average.Wait a minute, does that make sense? Let me double-check my calculations to be sure I didn't make any mistakes. So, 8 times 478 should equal 3,824.Let's multiply 8 by 400 first. 8 times 400 is 3,200. Then, 8 times 70 is 560, and 8 times 8 is 64. Adding those together: 3,200 plus 560 is 3,760, and then plus 64 is 3,824. Yep, that checks out.So, it looks like my calculation is correct. Each book in the science fiction section has 478 pages on average.
❓Given the function f(x) = log(a^x - b^x), where constants a and b satisfy a > 1 > b > 0, and a - b = 1, then the solution set for f(x) > 0 is ( )A: (0, +infty)B: (1, +infty)C: (2, +infty)D: (10, +infty)
💡Okay, so I have this problem where I need to find the solution set for the inequality ( f(x) > 0 ) where ( f(x) = log(a^x - b^x) ). The constants ( a ) and ( b ) satisfy ( a > 1 > b > 0 ) and ( a - b = 1 ). The options given are intervals starting from 0, 1, 2, or 10 to infinity. Hmm, let me try to break this down step by step.First, I know that the logarithm function ( log ) is only defined when its argument is positive. So, for ( f(x) ) to be defined, ( a^x - b^x ) must be greater than 0. That gives me the condition ( a^x > b^x ). Since ( a > 1 ) and ( 0 < b < 1 ), I can think about how these exponential functions behave.Exponential functions with bases greater than 1 grow as ( x ) increases, while exponential functions with bases between 0 and 1 decay as ( x ) increases. So, ( a^x ) will increase and ( b^x ) will decrease as ( x ) becomes larger. That suggests that ( a^x - b^x ) will also increase as ( x ) increases. Wait, but what about when ( x ) is negative? If ( x ) is negative, ( a^x ) becomes ( 1/a^{-x} ), which is a number between 0 and 1, and ( b^x ) becomes ( 1/b^{-x} ), which is a number greater than 1 because ( b < 1 ). So, for negative ( x ), ( a^x ) is less than ( b^x ), meaning ( a^x - b^x ) would be negative. Therefore, ( f(x) ) is not defined for negative ( x ). So, ( x ) must be positive.Now, moving on to the inequality ( f(x) > 0 ). Since ( f(x) = log(a^x - b^x) ), the inequality becomes ( log(a^x - b^x) > 0 ). I remember that ( log(y) > 0 ) when ( y > 1 ). So, this translates to ( a^x - b^x > 1 ).So, I need to solve ( a^x - b^x > 1 ). Given that ( a - b = 1 ), maybe I can use that somehow. Let me think about specific values of ( x ).When ( x = 1 ), ( a^1 - b^1 = a - b = 1 ). So, at ( x = 1 ), ( a^x - b^x = 1 ). Therefore, ( f(1) = log(1) = 0 ). So, at ( x = 1 ), the function equals zero.Since ( a > 1 ) and ( 0 < b < 1 ), as ( x ) increases beyond 1, ( a^x ) will grow exponentially, and ( b^x ) will decay exponentially. Therefore, ( a^x - b^x ) will increase as ( x ) increases beyond 1. That means that for ( x > 1 ), ( a^x - b^x > 1 ), so ( f(x) = log(a^x - b^x) > 0 ).What about when ( x ) is between 0 and 1? Let's pick ( x = 0.5 ). Then, ( a^{0.5} = sqrt{a} ) and ( b^{0.5} = sqrt{b} ). Since ( a > 1 ), ( sqrt{a} > 1 ), and since ( b < 1 ), ( sqrt{b} < 1 ). So, ( a^{0.5} - b^{0.5} ) is greater than ( a - b ) because ( a^{0.5} > a ) when ( a > 1 ) and ( b^{0.5} < b ) when ( b < 1 ). Wait, is that correct?Hold on, actually, for ( a > 1 ), ( a^{0.5} < a ) because the square root of a number greater than 1 is less than the number itself. Similarly, for ( b < 1 ), ( b^{0.5} > b ) because the square root of a number between 0 and 1 is greater than the number itself. So, ( a^{0.5} - b^{0.5} ) would be less than ( a - b ) because ( a^{0.5} < a ) and ( b^{0.5} > b ). Therefore, ( a^{0.5} - b^{0.5} < a - b = 1 ). So, ( a^{0.5} - b^{0.5} < 1 ), which means ( f(0.5) = log(a^{0.5} - b^{0.5}) < log(1) = 0 ). So, for ( x ) between 0 and 1, ( f(x) < 0 ).Similarly, when ( x = 1 ), ( f(x) = 0 ), and for ( x > 1 ), ( f(x) > 0 ). So, the solution set is ( x > 1 ), which is the interval ( (1, +infty) ).Let me double-check this reasoning. Since ( a^x ) is increasing and ( b^x ) is decreasing, their difference ( a^x - b^x ) is increasing. At ( x = 1 ), it's exactly 1, so the logarithm is zero. For ( x ) greater than 1, the difference becomes greater than 1, making the logarithm positive. For ( x ) less than 1, the difference is less than 1, making the logarithm negative. Therefore, the solution set should indeed be ( (1, +infty) ).I think that makes sense. So, the correct answer should be option B.**Final Answer**boxed{B}
❓If c is 20 % of a and a certain percent of b, then b is 200% of a. What percent of b is c?
💡First, I recognize that c is 20% of a, which can be expressed as c = 0.20 * a.Next, I know that b is 200% of a, so b = 2.00 * a.Since c is also a certain percentage of b, I can write c = (x/100) * b, where x is the percentage we need to find.Substituting the expression for b into this equation gives c = (x/100) * (2.00 * a).Now, I can set this equal to the earlier expression for c: 0.20 * a = (x/100) * (2.00 * a).By dividing both sides by a, I simplify the equation to 0.20 = (x/100) * 2.00.Multiplying both sides by 100 to eliminate the fraction results in 20 = 2x.Finally, dividing both sides by 2 gives x = 10.Therefore, c is 10% of b.
❓Let f(x) = Ax + B and g(x) = Bx + A, where A neq B. If f(g(x)) - g(f(x)) = 2(B - A), what is A + B?
💡Okay, so I have this problem here: there are two functions, f(x) = Ax + B and g(x) = Bx + A, where A is not equal to B. The condition given is that f(g(x)) minus g(f(x)) equals 2 times (B minus A). I need to find the value of A + B.Hmm, let me start by understanding what f(g(x)) and g(f(x)) mean. These are compositions of functions. So, f(g(x)) means I plug g(x) into f(x), and g(f(x)) means I plug f(x) into g(x). Then, I subtract these two results and set it equal to 2(B - A). Alright, let's compute f(g(x)) first. Since f(x) is Ax + B, and g(x) is Bx + A, substituting g(x) into f(x) gives me f(g(x)) = A*(g(x)) + B. So that's A*(Bx + A) + B. Let me expand that: A*Bx + A*A + B, which simplifies to ABx + A² + B.Now, let's compute g(f(x)). Similarly, g(f(x)) is B*(f(x)) + A. Since f(x) is Ax + B, substituting that in gives B*(Ax + B) + A. Expanding that, it's B*Ax + B*B + A, which simplifies to ABx + B² + A.So now I have f(g(x)) = ABx + A² + B and g(f(x)) = ABx + B² + A. The problem says that f(g(x)) minus g(f(x)) equals 2(B - A). Let me write that out:ABx + A² + B - (ABx + B² + A) = 2(B - A)Let me simplify the left side. The ABx terms cancel out because they are the same in both f(g(x)) and g(f(x)). So, I'm left with A² + B - B² - A. So, A² + B - B² - A = 2(B - A). Let me rearrange this equation to group like terms. I can write it as A² - B² + B - A = 2(B - A). Hmm, I notice that A² - B² is a difference of squares, which can be factored as (A - B)(A + B). So, let's factor that part:(A - B)(A + B) + (B - A) = 2(B - A)Wait, B - A is the same as -(A - B), so I can rewrite the equation as:(A - B)(A + B) - (A - B) = 2(B - A)Now, I can factor out (A - B) from the left side:(A - B)(A + B - 1) = 2(B - A)But 2(B - A) is the same as -2(A - B). So, substituting that in:(A - B)(A + B - 1) = -2(A - B)Since A ≠ B, (A - B) is not zero, so I can divide both sides by (A - B):A + B - 1 = -2Now, solving for A + B:A + B - 1 = -2 A + B = -2 + 1 A + B = -1Wait, that doesn't seem right. Let me double-check my steps. Starting from:(A - B)(A + B) + (B - A) = 2(B - A)I factored A² - B² as (A - B)(A + B), which is correct. Then, I noticed that B - A is -(A - B), so the equation becomes:(A - B)(A + B) - (A - B) = 2(B - A)Then, factoring out (A - B):(A - B)(A + B - 1) = 2(B - A)But 2(B - A) is indeed -2(A - B), so substituting:(A - B)(A + B - 1) = -2(A - B)Since A ≠ B, I can divide both sides by (A - B):A + B - 1 = -2Then, adding 1 to both sides:A + B = -1Wait, but earlier I thought I got -2. Maybe I made a mistake in the initial steps. Let me go back.Original equation after simplifying f(g(x)) - g(f(x)):A² - B² + B - A = 2(B - A)Which is:(A - B)(A + B) + (B - A) = 2(B - A)Factor out (A - B):(A - B)(A + B - 1) = 2(B - A)But 2(B - A) = -2(A - B), so:(A - B)(A + B - 1) = -2(A - B)Divide both sides by (A - B):A + B - 1 = -2So, A + B = -1Wait, so the correct answer should be A + B = -1?But in the initial problem, the user had a different thought process leading to A + B = -2. Maybe I need to check again.Let me recompute f(g(x)) and g(f(x)).f(g(x)) = A*(Bx + A) + B = ABx + A² + Bg(f(x)) = B*(Ax + B) + A = ABx + B² + ASubtracting: f(g(x)) - g(f(x)) = (ABx + A² + B) - (ABx + B² + A) = A² - B² + B - ASet equal to 2(B - A):A² - B² + B - A = 2(B - A)Factor A² - B² as (A - B)(A + B):(A - B)(A + B) + (B - A) = 2(B - A)Note that (B - A) = -(A - B), so:(A - B)(A + B) - (A - B) = 2(B - A)Factor out (A - B):(A - B)(A + B - 1) = 2(B - A)But 2(B - A) = -2(A - B), so:(A - B)(A + B - 1) = -2(A - B)Divide both sides by (A - B) (since A ≠ B):A + B - 1 = -2Thus, A + B = -1So, the correct answer should be A + B = -1, not -2 as initially thought.Wait, but in the initial problem, the user concluded A + B = -2. So, perhaps there was a miscalculation there.Let me verify the steps again.Starting from:A² - B² + B - A = 2(B - A)Factor A² - B² as (A - B)(A + B):(A - B)(A + B) + (B - A) = 2(B - A)Note that (B - A) = -(A - B):(A - B)(A + B) - (A - B) = 2(B - A)Factor out (A - B):(A - B)(A + B - 1) = 2(B - A)But 2(B - A) = -2(A - B):(A - B)(A + B - 1) = -2(A - B)Divide both sides by (A - B):A + B - 1 = -2Thus, A + B = -1Yes, so the correct answer is A + B = -1.I think the initial thought process had an error in the factoring step, leading to an incorrect conclusion of -2. The correct answer should be -1.