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Suppose the integer 7a.11a+1 has 42 positive divisors. What is the value of a?Select one:a.5b.None of the othersc.21d.7e.6

Question

Suppose the integer 7a.11a+1 has 42 positive divisors. What is the value of a?

Select one:

  • a. 5
  • b. None of the others
  • c. 21
  • d. 7
  • e. 6
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Solution

The number 7a.11a+1 can be rewritten as 7^a * 11^(a+1). The number of divisors of a number in prime factorization form (p1^e1 * p2^e2 * ... * pn^en) is (e1+1)(e2+1)...(en+1).

Given that 7a.11a+1 has 42 divisors, we can set up the equation (a+1)(a+2) = 42.

Solving this equation gives a = 5 or a = -7.

Since a cannot be negative in this context, the value of a is 5.

So, the correct answer is a.5.

This problem has been solved

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