Math Problem Statement

Suppose sum of two smallest positive divisors of an integer N is 6, while the sum of the two largest positive divisors of N is 858. What is the sum of the digits of N?

  1. 13

  2. 15

  3. 17

  4. 19

Solution

Let's analyze the given conditions step by step.

Step 1: Understanding the problem

  • Condition 1: The sum of the two smallest positive divisors of NN is 6.
  • Condition 2: The sum of the two largest positive divisors of NN is 858.
  • We need to find the sum of the digits of NN.

Step 2: Determine the smallest divisors

The smallest positive divisor of any integer is always 1. Let the second smallest divisor be dd. Therefore: 1+d=6    d=51 + d = 6 \implies d = 5 Thus, the two smallest divisors are 1 and 5.

Step 3: Determine the form of NN

Since 5 is a divisor of NN, NN must be a multiple of 5.

Step 4: Determine the largest divisors

The largest divisor of any number is the number itself, NN. Let the second largest divisor be N/dN/d', where dd' is another divisor of NN. According to the problem: N+Nd=858N + \frac{N}{d'} = 858 Rewriting the equation: N(1+1d)=858    N(d+1d)=858N \left(1 + \frac{1}{d'}\right) = 858 \implies N \left(\frac{d' + 1}{d'}\right) = 858 Thus, N=858dd+1N = \frac{858 \cdot d'}{d' + 1}

Step 5: Testing divisors

To solve for NN, we need to find suitable dd' such that NN is a multiple of 5. Testing values of dd':

  • For d=5d' = 5: N=85855+1=42906=715N = \frac{858 \cdot 5}{5 + 1} = \frac{4290}{6} = 715 Thus, N=715N = 715.

Step 6: Verify the conditions

  1. Smallest divisors: 1 and 5 (sum is 6).
  2. Largest divisors: 715 and 7155=143\frac{715}{5} = 143 (sum is 858).

Both conditions are satisfied.

Step 7: Sum the digits of NN

The sum of the digits of 715715 is: 7+1+5=137 + 1 + 5 = 13

Answer

The sum of the digits of NN is: 13\boxed{13}

Correct Option:

01) 13

Would you like further details on any step, or have any questions?

Relative Questions:

  1. What is the importance of divisors in number theory?
  2. How can we systematically find all divisors of a number?
  3. Why is 1 always considered the smallest divisor of any integer?
  4. How does factoring help in solving divisor-related problems?
  5. Can the problem be solved using a different approach?

Tip:

When solving problems involving divisors, always consider both small and large divisors, as their relationships often reveal useful patterns.

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Math Problem Analysis

Mathematical Concepts

Number Theory
Divisors
Multiples

Formulas

Sum of two smallest divisors: 1 + d = 6
Sum of two largest divisors: N + (N/d') = 858
Sum of digits formula

Theorems

Basic divisor theorem
Divisibility rules

Suitable Grade Level

Grades 9-12