Multiplying by a one-digit number · Usually met around P3
Estimate first, then work it out
Estimate first, then see if the answer is close.
How to do it
Method
Estimate first, then see if the answer is close
48 × 6 ≈ 50 × 6 = 300, so 288 is reasonable
Another way
Between two numbers
40 × 6 = 240, 50 × 6 = 300: the answer lies between
In full
Estimating means using easy, nearby numbers first, to see roughly how big the answer is. Round the number being multiplied to the nearest ten (or hundred): 48 is close to 50, so 48 × 6 is about 50 × 6 = 300. Then work out the exact answer, 288, and compare: close means reasonable; far off (a zero too many or too few, say) means work it out again. Or find which two numbers the answer lies between: 48 is between 40 and 50, so 48 × 6 is between 240 and 300.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Round 46 to the nearest ten. About how much is 46 × 2?
Show the answer and working
Answer: 100
The nearest ten to 46 is 50: 50 × 2 = 100.
Example 2
Between which two numbers does 54 × 7 lie?
- A. Between 3500 and 4200
- B. Between 420 and 490
- C. Between 350 and 420
- D. Between 280 and 350
Choose the right answer
Show the answer and working
Answer: C. Between 350 and 420
54 lies between two tens, so 54 × 7 lies between 350 and 420.
Example 3
Round 315 to the nearest hundred. About how much is 315 × 4?
Show the answer and working
Answer: 1200
The nearest hundred to 315 is 300: 300 × 4 = 1200.
Practise it in the game →Multiplying by a one-digit number · Free to start, unlimited questions, no download