Mastery: Reasoning and Problem-Solving

+20
54
6797
54+40=84
76-30=73
23+50=28
64-40=20


In-depth Investigation: The Number Square!
Focus on strategies involving adding/subtracting multiples of 10 to put numbers back in the correct place on the 100-grid, e.g. 14 + 40 = 54, 87 - 60 = 27. The Number Square! from nrich.maths.org.