Subtraction with Objects

Arithmetic · Axiom Academy

Remove counters from a group to model subtraction as taking away. Subtraction is the operation of taking away . Start with a group of objects, remove some of them, and count what's left — that count is the answer. You don't have to take that on faith: first watch a group lose a few counters, then run the removing yourself. Watch a group of 8 counters lose 3 of them, one at a time. As each counter flies away the equation fills in, settling on how many remain: 8 − 3 = 5 . Taking away 3 counters leaves 5 — that remaining count is the difference. Build a group, then take counters away Set a starting number of counters with the slider, then click a counter to remove it . The equation keeps track of where you started, how many you've taken away, and how many remain. Every counter you click is one taken from the group — and the answer is whatever stays behind. Start with 8 counters. Slide to choose how many to take away, and watch the equation 8 − (how many) = (how many left) settle. Counting what remains is the same as counting backward from 8. Take away all 8 and nothing is left; take away 0 and the whole group stays — every amount in between is a subtraction fact. You watched a group shrink, took counters away yourself, and read the answer straight off what remained. That is all subtraction is: start with an amount, take some away, and count what's left.

This is the written version of the interactive lesson above. See the full Arithmetic course.