Question

Arabella wants to buy 42 dresses.

Each dress costs £8.70.
Estimate the cost of Arabella's 42 dresses

Answer 1

378 Euros

Explanation:

A good way to estimate is to round to the nearest whole number or 10th and then multiply:

8.70 --> 9.00 (since 7 > 5 you round up to the nearest whole number, in this case 9)

then you multiply. A good way to do this in your head is doing:

split 42 into 2 numbers:
40, 2

then multiply by nine:

9 * 4 = 36 (9 * 40 = 360) added a zero since we multiplied by 40, its just easier to multiply by smaller numbers

9 * 2 = 18

then add the two numbers together:

360 + 18 = 378 Euros

The actual answer with a calculator is 365.4 Euros, so for an estimation its fairly close.

Another way you could solve it is to just round 8.70 --> 10 (rounding to the nearest 10th)

then:

10 * 42 = 420 (nice)

I don't recommend it since its way too off from the original value, but could be good for quick estimations.

hope this helped you :)