40 is 4 tens. So 6 × 40 is 6 × 4 tens, which is 24 tens. 24 tens is 240. You use a fact you already know, then make it ten times bigger.
A quick way: multiply the digits, then put one zero on the end. 7 × 30: 7 × 3 = 21, so 7 × 30 = 210. This works because multiplying by 10 moves every digit one place to the left.
Worked example
8 × 50 =
- 8 × 5 = 40.
- 50 is ten times 5, so the answer is ten times 40.
Answer:400
Key words
- multiple of 10
- a number like 20, 30 or 40
- tens
- groups of ten
- place value
- the value of a digit's position
Practise this
New questions every time.
Common Core-referenced: 3.NBT.A.3