Question

sum of all 3digit natural number which are divisible by 7

Answer 1

Hey user !!

Here is your answer !!

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List of three digit numbers divisible by 7 are 105,112.....994

It's clear that the above numbers are in AP

Hence a=105
d=7
an=994

Applying the formula

a + (n-1) d= 994

105 + (n-1) 7= 994

105+7n-7=994

98+7n=994

n=128

Now,

Sn=n/2(2a+(n-1)d)

Sn=128/2 ((2(105)+(128-1)7))

Sn=64(1099)=70336

Hope it is satisfactory :-)

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Answer 2

3+5+7=14 which 8s divisible by 7