The number of terms between 11 and 100 which are divisible by 7 but not by 3

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DSSSB Pharmacist 2014: Previous Year Paper
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  1. 08
  2. 09
  3. 27
  4. 28

Answer (Detailed Solution Below)

Option 2 : 09

Detailed Solution

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Given:

We need to find the number of terms between 11 and 100 that are divisible by 7 but not by 3.

Formula used:

For numbers divisible by 7:

The first term (A₁) = 14 (smallest number divisible by 7)

The last term (Aₙ) = 98 (largest number divisible by 7)

Number of terms divisible by 7 = (Aₙ - A₁)/7 + 1

Then, we subtract those divisible by both 7 and 3 (i.e., divisible by 21).

Calculations:

Number of terms divisible by 7:

(98 - 14)/7 + 1 = 13 terms

Numbers divisible by 21 (between 11 and 100):

The terms are 21, 42, 63, 84 = 4 terms

Final count:

13 - 4 = 9 terms

∴ The number of terms is 9.

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