Help me with this question please....

Question

Mohammed Safwat 2017-12-11

编辑： Roger Stafford 2017-12-11

Write a loop to calculate the sum 1*2+2*3+3*4+ ... + 99*100. The answer is 333300

so far I have

total = 0;
for n = 1:100;
    total = total + n;
end
fprintf('Total %d\n' , total)

Answer 1

John D'Errico 2017-12-11

编辑：John D'Errico 2017-12-11

Your loop sums only the integers from 1 to n, not the product of consecutive integers. But, hey, you were close, and you made a credible effort.

total = 0;
for n = 1:99
    total = total + n*(n+1);
end
fprintf('Total %d\n' , total)

There was actually a second problem with what you wrote. The desired sum will have only 99 terms to sum! So my loop goes only from 1 to 99.

Mohammed Safwat 2017-12-11

Thanks John!

Answer 2

Roger Stafford 2017-12-11

编辑：Roger Stafford 2017-12-11

An alternative formula which reduces the amount of computation would be:

n = 99;
total = n*(n+1)*(n+2)/3;

That is true for any positive integer n.