How do you work out 2/5 x 20?

[Scion286]

DS is in year 6, he did this today in school and knows that the answer is 8 but can’t remember the method. He said he found it really hard until the teacher explained it but he’s kicking himself now that he can’t remember how to work it out. Can anyone do it for us? I’m useless!

2/5 = two fifths = 0.4

0.4 multiplied by 20 = 8

Does the first bit make sense or do I need to expand?

Err, I'd think what's 1/5 or 20% of.20 and then double it. Probably not helpful.

Oh here you go:

www.bbc.co.uk/bitesize/topics/znmtsbk/articles/z4ymtv4

Thanks but he says no that’s not the way they did it in class.

I would say (to my yr5) that 1/5th is 4 (20/5) so 2/5ths is 8.

Divide 20 by 5 and then times by 2. Don’t over complicate the fraction, it just means x2 divide by 5

I would explain it as

To find 2/5 you first need to find 1/5 which means dividing 20 into 5 equal “portions”

20/5 = 4

But you wanted 2/5 so you need to multiply by 2 to give you the answer of 8

Did he divide 2 by 5?

20/5 = 4 x 2 = 8 is how I’d do it

Ha! I thought it was going to be a thread about PT working patterns.

Did he rearrange it to 2 x 20/5 ?

2/5 x 20 is the same as 2 x 20/5, where 20/5 = 4
2 x 4
8

Is he learning about converting fractions and decimals or is he learning about equations?

User1394 that’s the way, he says thank you very much!

Thanks everyone.

20 is actually 20/1

Multiply the top parts of the fraction together 2x20
Then multiply the bottom parts together 5x1

Then you have 40/5 - which is 8

With fractions what you are actually doing is dividing the top number by the bottom number. When you are working out a sum, you can do multiplication and division in any order. So 2/5 x 20 is the same as (2 x 20)/5 = 40/5 = 8. Or indeed the same as 2 x 20/5 = 2 x 4 = 8

Pleased to have helped

You have to imagine the 20 is divided by 1

So the sum is

2 x 20
5 1

So times the top 40
Times the bottom 5

40/5 is 8

@User1394

Divide 20 by 5 and then times by 2. Don’t over complicate the fraction, it just means x2 divide by 5

This.

Year 6 teacher here

I'd say: you know when we multiply fractions we multiply the numerators then you multiply the denominators. You need a denominator for 20. 20 means 20 whole ones so it is 20/1
So you are doing 2x20 = 40
And 5x1 =5
Your fraction is 40/5
We don't like improper fractions where the top is heavier than the bottom so we need to see how many times 5 fits into 40. It fits into 40, 8 complete times with no parts left over. So your answer is the whole number - (or integer) of 8.