KS2 maths homework - help!

Ivrytwr3

A kilo of meat is £8.60. I buy 400g. How much change from £10?

How would you do this sum?

I would say find how much 1g costs then multiply by 400 - you then know how much you have spent, then subtract that from the £10?

I have had a few different ways from different people!

liney

Find the cost of 100g by dividing by 10 because there are 1000g in a kg. From this you can then work out how much 400g costs - X4.
Finally subtract the cost from the £10.

8.60/10 is 0.86 per 100g x 4 = 3.44.
10.00 - 3.44 = 6.56 so £6.56 change.

Tropez

You just need to find the cost per 100grams which is 8.6/10. Once you've multiplied that result by 4 you have the price you pay and then it is a simple deduction.

Edit: Beaten to it.

Ivrytwr3

ha! I was trying to take it down to how much 1g costs!

mountainofdebt

To find the cost of the meat I would have divided by 10 and then multiplied by 4.

Then as you say taken the cost away from £10.

Does this have to be done mentally or written down by the way?

Twopints

£8.60 x 0.4 (i.e. 400/1000gm ) = 0.86 x 4 = £3.44, subtract from £10
:beer:

lammy82

You don't have to go via 100g or 1g; you know that 400g is four tenths of 1 kilo. So multiply the cost of a Kilo by 0.4 and you get the cost for 400g.

Then subtract the result from 10.

8.6 * 0.4 = 3.44
10 - 3.44 = 6.56

lammy82

Twopints wrote: »

£8.60 x 0.4 (i.e. 400/1000gm ) = 0.86 x 4 = £3.44, subtract from £10
:beer:

Yeah, like that

rachiibell

You need to see how the school are teaching sums like this. Different generations are often taught different ways but it can be confusing for the child if you explain everything differently to how their teacher did.

Ivrytwr3

written down and needs to show working out.

jackomdj

Actually there are many right ways to get to the answer.

What the teacher is after is seeing the workings so they know you have chosen a method. If it was an exam with say 10 marks you would still get marks even if you got one of the earlier parts of the sum wrong.