Multiplying by a one-digit number · Usually met around P3
Multiplying tens and hundreds by one digit
Multiply the tens digit, then put the 0 back.
How to do it
Method
Multiply the tens digit, then put the 0 back
30 × 4: 3 tens × 4 = 12 tens = 120
Another way
Add it up
30 + 30 + 30 + 30 = 120
In full
A whole number of tens is so many tens: 30 is 3 tens. 30 × 4 is 3 tens times 4, which makes 12 tens, that is 120. So work out 3 × 4 = 12 from the times tables, then put the 0 back on the end. Hundreds work the same way: 300 × 4 is 3 hundreds times 4, 12 hundreds, that is 1200, with two 0s on the end. Careful with 50 × 4: 5 × 4 = 20 already ends in 0, and one more 0 makes 200. Another way is to add: 30 × 4 = 30 + 30 + 30 + 30 = 120. A two-digit number times one digit can be split into tens and ones, each multiplied and then added: 23 × 3 = 20 × 3 + 3 × 3 = 60 + 9 = 69.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
400 × 7 = □
Show the answer and working
Answer: 2800
4 hundreds times 7 is 28 hundreds: 4 × 7 = 28, then two 0s, 2800.
Example 2
24 × 2 = 20 × 2 + 4 × 2 = □ + □ = □
Fill in each box
Show the answer and working
Answer: 40，8，48
Tens: 20 × 2 = 40; ones: 4 × 2 = 8; 40 + 8 = 48.
Example 3
40 × 9 = 360
True or false?
Show the answer and working
Answer: True
4 tens times 9: 40 × 9 = 360.
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