Grade 5 · Unit 1: Number and place value

Mental subtraction

Count up, compensate, use complements.

The Jamuna is one of Bangladesh’s great rivers.

River lengths

River lengths can be compared by subtraction. Mental strategies make it fast. Let us practise with large numbers and decimals.

Counting up with decimals

Count up from 3.75 to 4: 0.25. From 4 to 6: 2. Difference: 2.25.

Compensating

2.9 is nearly 3. Subtract 3, then add back the extra 0.1. Answer: 4.4.

Large numbers

365 thousand + 635 thousand = 1000 thousand. So 1 000 000 − 365 000 = 635 000. Think in thousands.

What I learnt