Same gap, moved along
Today I can explain that a difference stays the same when both numbers change by the same amount.
A Look back3 min
- 1.
90 − 40 =
- 2.
93 39
- 3.
There are 4 rows of 5 counters. 8 counters are taken away. How many are left?
B Watch me, then you4 min
34 − 19 = 15.
Add 1 to both numbers: 35 − 20.
The gap is still 15, so 35 − 20 = 15.
- 1.
42 − 27 = . Add 3 to both numbers first.
C Your turn5 min
- 1.
30 − 10 =
- 2.
35 − 15 =
- 3.
40 − 20 =
- 4.
45 − 25 =
Say it out loud: What changed in each row, and what stayed the same?
D Spot the mistake3 min
- 1.
What is 61 − 21?
E Think deeper4 min
- 1.
Two numbers have a difference of 45. Both go up by 300. Write the new difference and say why.