Check with the Opposite

Check subtraction with addition, and addition with subtraction.

Warm-up, learn, try it together, practice, then a quick check. About 15 minutes.

What children learn in Level 33

Adding and subtracting are opposites. One undoes the other! 34 and 28 make 62, so 62 minus 28 is 34.
To check 62 minus 28 equals 34, add back what you took away: 34 plus 28. You get 62, so it's right!
To check an addition, subtract. 45 plus 27 is 72. Check: 72 minus 27 is 45. Right!
Oops! Someone says 52 minus 17 is 45. Check: 45 plus 17 is 62, not 52. So 45 is wrong. The real answer is 35.
Checking with the opposite catches mistakes. Smart mathematicians always check!

Georgia's K-12 Mathematics Standards:

2.NR.2.4 — Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.