Help please - How do I do this sum? (or rather how should DS do it?)

[cottonwoolbrain]

This should be so easy but I can't seem to work it out at all let alone explain it to an 8 year old. Almost ashamed to ask:

If 250g of butter costs £2 how much is 15g?

I'm not even sure where to start let alone how to explain it to someone else.

Please can someone put it into nice simple steps for me ? I have a feeling it should be perfectly easy but... my brain is frazzled.

Divide 200 (£2) by 250, then times by 15. Is he allowed a calculator?

£2 divide by 250 x 15

This might not be the best method, but...

Divide £2 by 250 to work out how much 1g of butter is so 200p divided by 250 = 0.8p per gramme

Then multiply by 15 to work out how much 15g is

0.8p x 15 = 12p

So 15g costs 12p

Thank you.

No calculator allowed sadly.

Seems so simple now you've all told me though should be an interesting sum without a calculator

First you need to work out how much it costs per gram of butter.

Without a calculator I would go down the route of working out how much is 5g. More steps than working out cost of 1g method, but no calculator needed.

250g costs 200p
so 25g costs 20p
so 5g costs 4p
So 15g costs 12p

There’s no way my (bright, top set in maths) 8 year old could do this without a lot of help by the way!

Are you sure you’ve read/written the numbers correctly?

PPs are right about the method but they’re difficult numbers for 8. I’d expect more to see if 250g costs £2 how much does 125g cost. Or 50g. Not 15.

Weird.

Sorry ignore my first line above! if no calculator allowed then working out cost of 1g is too hard... so 5g route is better.

If you can't use a calculator and you want to avoid the “0.8” i would suggest finding out how much 5g of butter cost (instead of 1g)
250g: 5 = 50
200p : 50 = 4
So 5g of butter cost 4p
To get from 5g to 15g you have to calculate x3
So 4p x 3 is 12p for 15g of butter.

Proportion questions often use multiples of 10 or 5.
If a pupil was struggling with this question I would use the following prompts:

"So 250g of butter (a standard block) costs 200p."

"Imagine cutting the block of butter into 10g cubes. How many would there be?" (25 because 25 x 10g = 250g)

"How much would each of those 10g cubes cost?" (200p divided by 25 = 8p)

"Now, if 10g of butter costs 8p, how much would 5g cost?" (half of 8p = 4p)

"and how much would 15g cost?" (8p + 4p = 12p)

I'd agree for 8 this is very difficult number wise? My 10 yo is only doing long division now. And never be embarrassed op, there are at least 10 other parents in your child's class wondering the same. AT LEAST! Every question I've ever asked so many others are thinking the same

Ive just asked my 9 year old.
He cancelled it down stepwise:
250g costs 200p
125g costs 100p
25g costs 20p
5g costs 4p
15g costs 12p

Thank you so much everyone.

Doing it by breaking it down into 5g he understood and was able to work through with me.

So grateful to you all - he still thinks his mum is great at maths... if only he knew