Question

Consider n=1:10.Summing numbers that are multiples of 4 and 7 give 19 (ie. 4+7+8=19). What would be the sum of these multiples from n=1500:7000?

Answer 1

sum of integers between 1500 and 7000 (including) which is divisible by 4 or 7 is 8352033, which is shown below in sample output 2.

Here is Matlab Code :

function main
    function s = g(ni, nf)
        x = 0;
        y = 0;
        z = 0;
        for n = ni : nf
            if(mod(n,4)== 0)     %sum of all integers which are divisible by 4
                x = x + n;
            end
            if(mod(n,7) == 0)      %sum of all integers which is divisible by 7
                y = y + n;
            end
            if((mod(n,4)==0) && (mod(n,7)==0))        %sum of all integers which is divisible by both 4 and 7
                z = z + n;
            end
        end
        s = x + y - z;          %sum of all integers which are divisible by 4 or 7, using inclusion exclusion principle
        fprintf("sum = %d\n",s);
    end
    g(1500,7000);
end

Here is c code:

#include <stdio.h>

long int sum(int ni, int nf)
{
    long int x,y,z;
    x=y=z=0;
    long int i = ni;
    while(i<=nf)
    {
       if(i%4 == 0)
           x+=i;
       if(i%7 == 0)
           y+=i;
       if((i%4 == 0) && (i%7 == 0))
           z+=i;
        i++;
    }
    return (x + y - z);
}
int main()
{
    int ni, nf;
    ni = 1500;
    nf = 7000;
    printf("sum of integers between %d and %d (including)\nwhich is divisible by 4 or 7 is : \n", ni, nf);
    printf("sum = %ld\n", sum(ni, nf));
}

Here is output of the code:

sample output 1:

sample output 2: