Mental Math Strategies:
Doubling:
69 + 69
70 + 70 = 140
140 - 2 = 138
Decomposing Numbers:
267 + 124
200 + 100 + 60 + 20 + 7 + 4
300 + 80 + 10 + 1 = 391
Magic Ten / Friendly Numbers
36 + 19
35 + 20 = 55
For grade 4, the curriculum expectation is using a variety of mental math strategies to add and subtract 2-digit numbers.
