Question

Sum of first 100 natural no which are not divisible 3 or 7

Answer 1

sum of 100 no 1-100 == u Know it 5050

Find sum of those which are div by 3 ,7 and both

3 =33 numbers    = 33/2 { 3+99}

7= 14 number = 14/2 { 7+ 98}

21= 4 =  21+42+63+84

total  sum   = 3 series + 7 series -21 series sum

1683+735-210 = 2208

5050-2208  =2842