Decimal calculations Use facts you know to calculate with decimals. Look at the numbers and decide on the best strategy to work out the answer. Use near doubles.
Count on or back in different jumps.
Example: What is 3.6 + 3.5?
Example: What is 9.2 − 6.8?
3.5 + 3.5 = 7
2.2 0.2
So, 3.5 + 3.6 = 7.1 6.8
7
9.2
9.2 − 6.8 = 2.4 Partition, or break numbers up.
Use facts you know.
Example: What is 4.8 × 5?
Example: What is 0.9 × 7?
4 × 5 = 20
9 × 7 = 63
0.8 × 5 = 4
So, 0.9 × 7 = 6.3
So, 4.8 × 5 = 24
Warm up 1
Choose the correct decimal answer from the box for each of these calculations. 3.5
34
2.4
12.6
a) 0.7 × 5
b) 0.8 × 3
c) 2.4 × 6
d) 1.4 × 9
e) 2.3 × 8
f) 4.1 × 5
g) 0.9 × 5
h) 1.8 × 6
10.8
14.4
18.4
4.5
20.5