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William Lowell Putnam Mathematical Competition

Description: Welcome to the William Lowell Putnam Mathematical Competition Quiz! This quiz is designed to test your knowledge and skills in various areas of mathematics, including algebra, calculus, geometry, and number theory. The questions are challenging and require critical thinking and problem-solving abilities. Good luck!
Number of Questions: 14
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Tags: mathematics mathematical competitions william lowell putnam mathematical competition
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Let (f(x) = x^3 - 3x^2 + 2x + 1). Find the value of (f(f(1))).

  1. 1

  2. 2

  3. 3

  4. 4


Correct Option: A
Explanation:

Given (f(x) = x^3 - 3x^2 + 2x + 1), we have (f(1) = 1^3 - 3(1)^2 + 2(1) + 1 = -1). Therefore, (f(f(1)) = f(-1) = (-1)^3 - 3(-1)^2 + 2(-1) + 1 = 1).

In a triangle (ABC), if (\angle A = 60^\circ), (\angle B = 75^\circ), and (\angle C = 45^\circ), find the ratio of the length of side (a) to the length of side (b).

  1. (\frac{1}{\sqrt{2}})

  2. (\frac{\sqrt{2}}{2})

  3. (\frac{\sqrt{3}}{2})

  4. (\frac{2}{\sqrt{3}})


Correct Option: B
Explanation:

Using the Law of Sines, we have (\frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}). Therefore, (\frac{a}{\sin 60^\circ} = \frac{b}{\sin 75^\circ}). Solving for (\frac{a}{b}), we get (\frac{a}{b} = \frac{\sin 60^\circ}{\sin 75^\circ} = \frac{\sqrt{3}}{2}).

Find the area of the region bounded by the curves (y = x^2 - 4x + 3) and (y = x - 1).

  1. 4

  2. 6

  3. 8

  4. 10


Correct Option: C
Explanation:

To find the area of the region, we need to find the points of intersection of the two curves. Solving (x^2 - 4x + 3 = x - 1), we get (x^2 - 5x + 4 = 0). Factoring, we get ((x - 1)(x - 4) = 0). Therefore, the points of intersection are ((1, 0)) and ((4, 3)). The area of the region is given by the integral (\int_1^4 (x^2 - 4x + 3) - (x - 1) \ dx). Evaluating the integral, we get (\frac{8}{3}).

Let (S) be the set of all positive integers less than 100 that are divisible by 3 or 5. Find the sum of all the elements of (S).

  1. 1050

  2. 1200

  3. 1350

  4. 1500


Correct Option: C
Explanation:

The elements of (S) are the multiples of 3 and 5 less than 100. The multiples of 3 are (3, 6, 9, ..., 99), and the multiples of 5 are (5, 10, 15, ..., 95). However, some numbers are counted twice, such as 15, which is a multiple of both 3 and 5. To find the sum of all the elements of (S), we need to subtract the sum of the numbers that are counted twice. The sum of the multiples of 3 is (3 + 6 + 9 + ... + 99 = \frac{33(100)}{2} = 1650), and the sum of the multiples of 5 is (5 + 10 + 15 + ... + 95 = \frac{20(100)}{2} = 1000). The sum of the numbers that are counted twice is (15 + 30 + 45 + ... + 90 = \frac{15(100)}{2} = 750). Therefore, the sum of all the elements of (S) is (1650 + 1000 - 750 = 1350).

Let (f(x) = \frac{x^2 - 1}{x - 1}). Find the value of (\lim_{x \to 1} f(x)).

  1. 0

  2. 1

  3. 2

  4. Does not exist


Correct Option: C
Explanation:

We can factor the numerator of (f(x)) as (x^2 - 1 = (x + 1)(x - 1)). Therefore, (f(x) = \frac{(x + 1)(x - 1)}{x - 1} = x + 1). Substituting (x = 1) into (f(x)), we get (f(1) = 1 + 1 = 2). Therefore, (\lim_{x \to 1} f(x) = 2).

Let (A) be a (3 \times 3) matrix with eigenvalues (1, 2, 3). Find the determinant of (A^2).

  1. 1

  2. 6

  3. 12

  4. 18


Correct Option: D
Explanation:

The determinant of a matrix is the product of its eigenvalues. Therefore, the determinant of (A) is (1 \cdot 2 \cdot 3 = 6). The determinant of (A^2) is the square of the determinant of (A), so the determinant of (A^2) is (6^2 = 18).

Find the number of positive integers less than 1000 that are divisible by 7 but not by 11.

  1. 125

  2. 132

  3. 139

  4. 146


Correct Option: B
Explanation:

The numbers that are divisible by 7 but not by 11 are the multiples of 7 that are not multiples of 11. The multiples of 7 less than 1000 are (7, 14, 21, ..., 994), and the multiples of 11 less than 1000 are (11, 22, 33, ..., 990). The numbers that are multiples of both 7 and 11 are (77, 154, 231, ..., 931). Therefore, the number of positive integers less than 1000 that are divisible by 7 but not by 11 is (\frac{994}{7} - \frac{990}{11} + \frac{931}{77} = 132).

Let (f(x) = \frac{x^3 - 1}{x - 1}). Find the value of (f'(2)).

  1. 1

  2. 2

  3. 3

  4. 4


Correct Option: B
Explanation:

We can use the quotient rule to find the derivative of (f(x)). The quotient rule states that if (f(x) = \frac{g(x)}{h(x)}), then (f'(x) = \frac{h(x)g'(x) - g(x)h'(x)}{h(x)^2}). In this case, (g(x) = x^3 - 1) and (h(x) = x - 1). Therefore, (g'(x) = 3x^2) and (h'(x) = 1). Substituting these values into the quotient rule, we get (f'(x) = \frac{(x - 1)(3x^2) - (x^3 - 1)(1)}{(x - 1)^2} = \frac{3x^3 - 3x^2 - x^3 + 1}{(x - 1)^2} = \frac{2x^3 - 3x^2 + 1}{(x - 1)^2}). Substituting (x = 2) into (f'(x)), we get (f'(2) = \frac{2(2)^3 - 3(2)^2 + 1}{(2 - 1)^2} = \frac{16 - 12 + 1}{1} = 2).

Let (A) be a (3 \times 3) matrix with eigenvalues (1, 2, 3). Find the trace of (A^3).

  1. 9

  2. 18

  3. 27

  4. 36


Correct Option: C
Explanation:

The trace of a matrix is the sum of its eigenvalues. Therefore, the trace of (A) is (1 + 2 + 3 = 6). The trace of (A^3) is the trace of (A \cdot A \cdot A), which is equal to the sum of the eigenvalues of (A \cdot A \cdot A). The eigenvalues of (A \cdot A \cdot A) are the cubes of the eigenvalues of (A), which are (1^3, 2^3, 3^3). Therefore, the trace of (A^3) is (1^3 + 2^3 + 3^3 = 1 + 8 + 27 = 36).

Let (S) be the set of all positive integers less than 100 that are divisible by 2 or 3. Find the sum of all the elements of (S).

  1. 1500

  2. 1650

  3. 1800

  4. 1950


Correct Option: C
Explanation:

The elements of (S) are the multiples of 2 and 3 less than 100. The multiples of 2 are (2, 4, 6, ..., 98), and the multiples of 3 are (3, 6, 9, ..., 99). However, some numbers are counted twice, such as 6, which is a multiple of both 2 and 3. To find the sum of all the elements of (S), we need to subtract the sum of the numbers that are counted twice. The sum of the multiples of 2 is (2 + 4 + 6 + ... + 98 = \frac{2(100)}{2} = 1000), and the sum of the multiples of 3 is (3 + 6 + 9 + ... + 99 = \frac{3(100)}{2} = 1500). The sum of the numbers that are counted twice is (6 + 12 + 18 + ... + 96 = \frac{6(100)}{2} = 300). Therefore, the sum of all the elements of (S) is (1000 + 1500 - 300 = 1800).

Let (f(x) = \frac{x^2 - 4x + 3}{x - 1}). Find the value of (f'(1)).

  1. -1

  2. 0

  3. 1

  4. 2


Correct Option: D
Explanation:

We can use the quotient rule to find the derivative of (f(x)). The quotient rule states that if (f(x) = \frac{g(x)}{h(x)}), then (f'(x) = \frac{h(x)g'(x) - g(x)h'(x)}{h(x)^2}). In this case, (g(x) = x^2 - 4x + 3) and (h(x) = x - 1). Therefore, (g'(x) = 2x - 4) and (h'(x) = 1). Substituting these values into the quotient rule, we get (f'(x) = \frac{(x - 1)(2x - 4) - (x^2 - 4x + 3)(1)}{(x - 1)^2} = \frac{2x^2 - 6x + 4 - x^2 + 4x - 3}{(x - 1)^2} = \frac{x^2 - 2x + 1}{(x - 1)^2}). Substituting (x = 1) into (f'(x)), we get (f'(1) = \frac{1^2 - 2(1) + 1}{(1 - 1)^2} = \frac{0}{(0)^2} = \infty).

Let (A) be a (3 \times 3) matrix with eigenvalues (1, 2, 3). Find the determinant of (A^4).

  1. 1

  2. 81

  3. 243

  4. 729


Correct Option: D
Explanation:

The determinant of a matrix is the product of its eigenvalues. Therefore, the determinant of (A) is (1 \cdot 2 \cdot 3 = 6). The determinant of (A^4) is the square of the determinant of (A^2), which is equal to the square of the determinant of (A \cdot A). The eigenvalues of (A \cdot A) are the squares of the eigenvalues of (A), which are (1^2, 2^2, 3^2). Therefore, the determinant of (A^2) is (1^2 \cdot 2^2 \cdot 3^2 = 36). The determinant of (A^4) is (36^2 = 729).

Let (S) be the set of all positive integers less than 100 that are divisible by 3 or 4. Find the sum of all the elements of (S).

  1. 1200

  2. 1350

  3. 1500

  4. 1650


Correct Option: C
Explanation:

The elements of (S) are the multiples of 3 and 4 less than 100. The multiples of 3 are (3, 6, 9, ..., 99), and the multiples of 4 are (4, 8, 12, ..., 96). However, some numbers are counted twice, such as 12, which is a multiple of both 3 and 4. To find the sum of all the elements of (S), we need to subtract the sum of the numbers that are counted twice. The sum of the multiples of 3 is (3 + 6 + 9 + ... + 99 = \frac{3(100)}{2} = 1500), and the sum of the multiples of 4 is (4 + 8 + 12 + ... + 96 = \frac{4(100)}{2} = 2000). The sum of the numbers that are counted twice is (12 + 24 + 36 + ... + 96 = \frac{12(100)}{2} = 600). Therefore, the sum of all the elements of (S) is (1500 + 2000 - 600 = 1500).

Let (f(x) = \frac{x^3 - 2x^2 + x - 2}{x - 2}). Find the value of (f'(2)).

  1. -1

  2. 0

  3. 1

  4. 2


Correct Option: C
Explanation:

We can use the quotient rule to find the derivative of (f(x)). The quotient rule states that if (f(x) = \frac{g(x)}{h(x)}), then (f'(x) = \frac{h(x)g'(x) - g(x)h'(x)}{h(x)^2}). In this case, (g(x) = x^3 - 2x^2 + x - 2) and (h(x) = x - 2). Therefore, (g'(x) = 3x^2 - 4x + 1) and (h'(x) = 1). Substituting these values into the quotient rule, we get (f'(x) = \frac{(x - 2)(3x^2 - 4x + 1) - (x^3 - 2x^2 + x - 2)(1)}{(x - 2)^2} = \frac{3x^3 - 6x^2 + x - 3x^2 + 8x - 2 - x^3 + 2x^2 - x + 2}{(x - 2)^2} = \frac{2x^3 - 7x^2 + 9x}{(x - 2)^2}). Substituting (x = 2) into (f'(x)), we get (f'(2) = \frac{2(2)^3 - 7(2)^2 + 9(2)}{(2 - 2)^2} = \frac{16 - 28 + 18}{0} = \infty).

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