Math Problem Statement

The number of divisors of 14700 which are divisible by 10 but not by 100 is

Solution

We are tasked with finding how many divisors of 14,700 are divisible by 10 but not by 100. Let's break this down step by step:

Step 1: Prime factorization of 14,700

We begin by finding the prime factorization of 14,700.

14,700=22×3×52×7214,700 = 2^2 \times 3 \times 5^2 \times 7^2

Step 2: Divisors divisible by 10

A number divisible by 10 must include at least 21×512^1 \times 5^1 in its prime factorization (since 10=2×510 = 2 \times 5).

To find divisors of 14,700 divisible by 10, we must focus on the divisors that contain at least one factor of 2 and one factor of 5.

Step 3: Divisors divisible by 100

A number divisible by 100 must include at least 22×522^2 \times 5^2 in its prime factorization (since 100=22×52100 = 2^2 \times 5^2).

We need to find the divisors that are divisible by 10 but not by 100, meaning we want divisors that contain at least one factor of 2 and one factor of 5, but not both 222^2 and 525^2.

Step 4: Counting the divisors divisible by 10 but not 100

We now break down the counting:

  1. Divisors divisible by 10:
    A divisor divisible by 10 must include 21×512^1 \times 5^1.
    Consider the prime factorization 22×3×52×722^2 \times 3 \times 5^2 \times 7^2.
    A divisor divisible by 10 can take:

    • 212^1 or 222^2 (two choices for the power of 2),
    • 515^1 or 525^2 (two choices for the power of 5),
    • Any power of 3: 303^0 or 313^1 (two choices),
    • Any power of 7: 707^0, 717^1, or 727^2 (three choices).

    So the total number of divisors divisible by 10 is:

    2×2×2×3=242 \times 2 \times 2 \times 3 = 24

  2. Divisors divisible by 100:
    A divisor divisible by 100 must include 22×522^2 \times 5^2.
    For divisors divisible by 100, we have:

    • Exactly 222^2 (one choice),
    • Exactly 525^2 (one choice),
    • Any power of 3: 303^0 or 313^1 (two choices),
    • Any power of 7: 707^0, 717^1, or 727^2 (three choices).

    So the total number of divisors divisible by 100 is:

    1×1×2×3=61 \times 1 \times 2 \times 3 = 6

Step 5: Subtract to find divisors divisible by 10 but not 100

The number of divisors divisible by 10 but not by 100 is:

246=1824 - 6 = 18

Thus, the number of divisors of 14,700 that are divisible by 10 but not by 100 is 18.

Would you like more details or have any questions?

Here are 5 related questions to consider:

  1. What is the number of divisors of 14,700 in total?
  2. How would the process change if we were looking for divisors divisible by 5 instead of 10?
  3. Can you find how many divisors of 14,700 are divisible by 7?
  4. What if we wanted divisors divisible by 20 but not by 200?
  5. How would you approach finding the sum of all divisors of 14,700?

Tip: When solving divisor problems, prime factorization is essential for breaking down the conditions and constraints efficiently.

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Math Problem Analysis

Mathematical Concepts

Number Theory
Divisibility
Prime Factorization

Formulas

Divisor Counting Formula

Theorems

Fundamental Theorem of Arithmetic

Suitable Grade Level

Grades 10-12