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question:Does there exist a strictly increasing function from the set of positive integers mathbb{N}^{*} to itself such that f(1)=2 and for every positive integer n, the following equation holds? f(f(n)) = f(n) + n (IMO 1993)

answer:**Objective:** We are to determine if there exists a function (f: mathbb{N}^* to mathbb{N}^*) that is strictly increasing and satisfies ( f(1) = 2 ) and for all ( n in mathbb{N}^* ): [ f(f(n)) = f(n) + n. ] **Approach:** Construct such a function by induction. **Steps:** 1. **Base case:** Define ( f(1) = 2 ). 2. **Induction hypothesis:** Assume we have defined ( f ) for all ( 1 leq k leq n ) such that ( f ) is strictly increasing and the given functional equation holds for all ( k leq n ). 3. **Inductive step:** Define ( f(n+1) ). We need ( f ) to be strictly increasing, so we begin by ensuring ( f(n+1) > f(n) ). We also need to satisfy the functional equation for ( n+1 ): [ f(f(n+1)) = f(n+1) + (n + 1). ] Let's denote a potential candidate for ( f(n+1) ) by ( a ), where ( a ) is such that ( f(n) < a ) and ( a ) adheres to the equation above. 4. **Constructing ( f(n+1) ):** - Define a helper function ( g ): [ g(n + 1) = max{ k in {1, ldots, n} mid f(k) leq n + 1 }. ] Since ( g(n + 1) ) ensures the maximum ( k ) with ( f(k) leq n + 1 ), and we know ( g(n + 1) ) exists because ( f(1) = 2 leq n+1 ). - Then set: [ f(n + 1) = g(n + 1) + n + 1. ] - By construction, this definition makes ( f ) strictly increasing because ( g(n + 1) geq g(n) implies f(n + 1) > f(n) ). 5. **Verification:** Now, verify if the functional equation holds: [ f(f(n + 1)) = f(g(n + 1) + n + 1). ] Given that ( g(f(n + 1)) = n + 1 ), we get: [ f(f(n + 1)) = f(n + 1) + (n + 1). ] - Check the base case consistency: - For ( f(1) = 2 ), ( f(f(1)) = f(2) = g(2) + 2 = 1 + 2 = 3 ), we have: [ f(f(1)) = 3 = 2 + 1 = f(1) + 1. ] - Inductive case consistency: - Assume ( f(n) ) is accurately defined. By construction, ( f(n+1) ) with ( g(f(n+1)) = n+1 ): [ f(f(n+1)) = f(n+1) + (n + 1). ] **Conclusion:** Thus, there exists a strictly increasing function ( f: mathbb{N}^* to mathbb{N}^* ) such that ( f(1) = 2 ) and ( f(f(n)) = f(n) + n ) for all ( n ). Therefore, the answer is: [ boxed{text{Yes}} ]

question:Find the sum of the first eight terms in the geometric sequence frac{1}{3}, frac{1}{9}, frac{1}{27}, dots.

answer:The geometric sequence given has a first term a_0 = frac{1}{3} and a common ratio r = frac{1}{3}. The number of terms, n, is 8. The sum S_n of the first ( n ) terms of a geometric sequence can be calculated using the formula: [ S_n = a_0 frac{1-r^n}{1-r} ] Substituting the known values: [ S_8 = frac{frac{1}{3}(1-left(frac{1}{3}right)^8)}{1-frac{1}{3}} = frac{frac{1}{3}(1-frac{1}{6561})}{frac{2}{3}} = frac{frac{1}{3} times frac{6560}{6561}}{frac{2}{3}} = frac{6560}{19683} ] Thus, the sum of the first eight terms of the sequence is: [ boxed{frac{6560}{19683}} ]

question:Convert the binary number 101111_{(2)} into a decimal number. A: 47 B: 56 C: 122 D: 64

answer:To solve, 101111_{(2)} = 1 times 2^5 + 0 times 2^4 + 1 times 2^3 + 1 times 2^2 + 1 times 2^1 + 1 times 2^0 = 47. Therefore, the correct option is boxed{A}. **Analysis:** By using 101111_{(2)} = 1 times 2^5 + 0 times 2^4 + 1 times 2^3 + 1 times 2^2 + 1 times 2^1 + 1 times 2^0, we can easily find the answer.

question:Dave weighs 175 pounds and can bench press three times his body weight. Craig can only bench press a certain percentage of the amount Dave can. Mark is new and can bench press 50 pounds less than Craig. Mark can bench press 55 pounds. What is the percentage of the amount Craig can bench press compared to Dave's bench press?

answer:First, let's calculate how much Dave can bench press. Since Dave can bench press three times his body weight and he weighs 175 pounds: Dave's bench press = 3 * 175 = 525 pounds Mark can bench press 55 pounds, and we know that Craig can bench press 50 pounds more than Mark: Craig's bench press = Mark's bench press + 50 = 55 + 50 = 105 pounds Now, to find the percentage of the amount Craig can bench press compared to Dave's bench press, we use the formula: Percentage = (Craig's bench press / Dave's bench press) * 100 Percentage = (105 / 525) * 100 Percentage = (1 / 5) * 100 Percentage = 0.2 * 100 Percentage = 20% So, Craig can bench press boxed{20%} of the amount Dave can bench press.

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