Grade 3 · Unit 1: Number and place value

Subtracting in your head

Count up, jump back or adjust.

How much further?

Dhaka to Chattogram is about 320 km by train. After 185 km, how far is left? We can find the difference in our heads.

Count up

Count up from 185 to 320. 185 → 200 is 15. 200 → 300 is 100. 300 → 320 is 20. 15 + 100 + 20 = 135 km left.

Jump back

Jump back the tens, then the ones. 475 − 40 = 435. 435 − 3 = 432. This works well when the number to subtract is small.

Round and adjust

98 is nearly 100. Take away 100, then add back the 2 you took too many. This is compensating for subtraction.

What I learnt

• I can count up to find a difference.
• I can jump back on a number line.
• I can round and adjust to subtract.