Question

Find the sum of 3 digit natural number which are divisible by7

Answer 1

list of 3 digit number which is divisible by 7  are 105,112,.............994
so,
a=105 , d=7 and an=994
then 
an=a+(n-1)d after putting values of a,d and an
u will get n=128
then Sn=n/2(2*a+(n-1)d)
after putting values of n,a and d..u will get the sum=70336

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