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Dividing by 0.5. How to divide quickly any number by one half (number math tricks)

Updated on June 19, 2013

Many people get caught out when they have to divide a number by 0.5 (most will wrongly half the original number). In fact, all you need to do is double the original number. This is because 0.5 is the same as one half and two halves make a whole! Imagine working out 4 ÷ 0.5 by going through your multiples of 0.5:

0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4...

As you can see you reach the number 4 on the 8th multiple of 0.5. And notice that 8 is twice the size of the original number.

Therefore, just double the original number if you are dividing by 0.5 (or multiply by 2 if easier).

Let’s look at some more examples which involve dividing by 0.5.

Example 1

Work out the value of 9 ÷ 0.5:

All you have to do is double 9:

9 + 9 = 18

Example 2

Work out the value of 26 ÷ 0.5:

All you have to do is double 26:

26 + 26 = 52.

Example 3

Work out the value of 105 ÷ 0.5:

Again, just double 105:

105 + 105 = 210

Example 4

Work out the value of 3428 ÷ 0.5:

Just like the last 3 examples just double 3428:

3428 + 3428 = 6856.

Example 5

Work out the value of -15 ÷ 0.5:

Even if you have a negative number just double the number:

-15 × 2 = -30

Example 6

Work out the value of 0.6 ÷ 0.5.

Again, just double the original number even if you have a decimal:

0.6 + 0.6 = 1.2

Example 7

Estimate (578 × 62.3)/0.549

This question is a little harder as you need to work out an approximate answer:

Round 578 to the nearest 100 which is 600.

Round 62.3 to the nearest 10 which is 60

Round 0.549 to the nearest 1/10 which is 0.5

Therefore to work out your estimate do (600 × 60) ÷ 0.5 = 36,000 ÷ 0.5. So to get you final answer double 36000 which gives you an answer of 72,000.

Summary

Dividing by 0.5 is the same as doubling or multiplying by 2.

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  • joanwz profile image

    Joan Whetzel 4 years ago from Katy, Texas

    Clever. I really love your math Hubs. Your explanations are easy to understand. Thanks.

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