The sum of all positive integers less than 400 which are not divisible by 5.

We will use the sum of natural number series formula

if S=1+2+3+4 + ... + n, then

S = n (n+1) / 2

Now, sum of all + ve integers from 0 to 400 is given by

S=0+1+2+3 + ... + 400

=> S=400 (400+1) / 2;

=>S=80200;

Sum of all + ve integers divisible by 5 is given by

R=0+5+10+15+20+25+30 + ... + 400

R=5 (1+2+3+4+5+6 + ... + 80)

R=5*80 (80+1) / 2

R=16200;

therefore the sum of all + ve integers <400 and not divisible by 5=S-R=64000