Word Problem :S

[lovely_nancy]

Joe Buys 18kg of potatoes. Some of these are old potatoes at 22p per kilogram, the rest are new ones at 36p per kilogram.
a) Denoting the weight of old potatoes he buys by "w" kg, write down an expression for the total cost of Joe's Potatoes.
b) Joe pays with a £5 note and receives 20p change. What weight of new potatoes does he buy?

What I can come up with is w*22 - 18*36
tell me if im correct please ...

 

[Mrspi]

Joe Buys 18kg of potatoes. Some of these are old potatoes at 22p per kilogram, the rest are new ones at 36p per kilogram.
a) Denoting the weight of old potatoes he buys by "w" kg, write down an expression for the total cost of Joe's Potatoes.
b) Joe pays with a £5 note and receives 20p change. What weight of new potatoes does he buy?

What I can come up with is w*22 - 18*36
tell me if im correct please ...

No, I'm sorry....but 22*w is the right number of "p" for the old potatoes.

If w = number of kg of "old potatoes" at 22p per kg, then 22w p is the cost of the old potatoes.

Would you agree with this?

cost of old potatoes + cost of new potatoes = total cost

If Joe bought 100 kg of potatoes in all, and "w" kg were old potatoes, how many kg of NEW potatoes did he buy?

And new potatoes cost 36p for each kg. So, the cost of the new potatoes will be 36p times the number of kg of new potatoes purchased.

Here's a hint: if you buy 10 kg of apples, and x kg are red apples, then (10 - x) kg would be the number of kg that are NOT red apples.

If Joe purchased a total of 100 kg of potatoes, and "w" kg were OLD potatoes, then what would be the number of kg of NEW potatoes?

 

[lovely_nancy]

But then how would we work out if he is paying £5 and gets 20p change
which means he pays £4:80 altogether then how do we work out what weight of potatoes he buys because
the amount in kg for the old and new potatoes is still hidden

 

[Denis]

Joe Buys 18kg of potatoes. Some of these are old potatoes at 22p per kilogram, the rest are new ones at 36p per kilogram.
a) Denoting the weight of old potatoes he buys by "w" kg, write down an expression for the total cost of Joe's Potatoes.
b) Joe pays with a £5 note and receives 20p change. What weight of new potatoes does he buy?
What I can come up with is w*22 - 18*36
tell me if im correct please ...

KEEP IT SIMPLE!
w = number @ 22 ; so 18-w = number @ 36
Amount spent = 480

22w + 36(18 - w) = 480

Solve that for w. If you can't, you need classroom help.