Let’s say we want to add up every number between 1 and 100.

1+2+3+4+5+6+7+….+100

That would take a while unless you rearrange the numbers.

1+100+2+99+3+98+4+97+5+96+….+51+50

which equals

101 +101 +101 + 101 + 101 +101 + 101 +… + 101

Now it’s a multiplication problem

101*50

1+2+3+4+5+6+7+….+100 = 5050