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