By William McCallum

You will never have to subtract again.

Students sometimes learn about addition and subtraction of integers using integer chips. These are circular chips, with a yellow chip representing +1 and a red chip representing -1. You start with the all-important rule that $1+\left(\text{–}1\right)=0$

$1 + (\text-1) = 0$
, so you can add or remove a red-yellow pair without changing the number. To calculate the right hand side of the equation in the title, $3+\left(\text{–}5\right)$

$3 + (\text-5)$
, you put 3 yellow chips together with 5 red chips, then remove 3 red-yellow pairs, leaving 2 red chips. So $3+\left(\text{–}5\right)=-2$

$3 + (\text-5) = -2$
.

Continue reading “Why is 3 – 5 = 3 + (-5)?” →