Aspire Faculty ID #16452 · Topic: NIMCET 2009 · Just now
NIMCET 2009

The sum of the numbers from 1 to 100 which are not divisible by 3 and 5 is:

Solution

Total sum: $S = \dfrac{100 \cdot 101}{2} = 5050$ 
Sum of multiples of 3 ≤100: 
$3 + 6 + \ldots + 99 = 1683$ 

Sum of multiples of 5 ≤100: 
$5 + \ldots + 100 = 1050$ 

Sum of multiples of 15 ≤100: 
$15 + \ldots + 90 = 315$ 

Numbers divisible by 3 or 5: 
$1683 + 1050 - 315 = 2418$ 
Required sum: $5050 - 2418 = 2632$

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