Karol bought 1lb of sugar. She used 1/4 lb of sugar to bake a big cake and some of the remaining sugar to make lots of cookies. She had 3/8 lb of sugar left. How much sugar did Karol use for the cookies?

I came up with 3/8-1/4=3/8-2/8=1/8 lb

Start with the whole amount, then subtract what was used. The result is what was left:

1 - 1/4 - x = 3/8
x = 3/8 for the cookies

why did you use 3/8 - 1/4?
3/8 is how much she had left, and 1/4 was for the cake. How does that tell you anything about the cookies?

Thought the difference of 3/8 and 1/4 would give the amount of sugar for cookies, but I see where where I went wrong. I needed to include the 1 pound of sugar and make 3/8 the total. Thank you very much.

Your calculation is correct! To find out how much sugar Karol used for the cookies, you subtract the amount of sugar used for the cake (1/4 lb) from the amount of sugar left (3/8 lb).

1/4 lb of sugar used for the cake
3/8 lb of sugar left

To find out how much sugar Karol used for the cookies, you subtract 1/4 lb from 3/8 lb.

3/8 lb - 1/4 lb = (3/8 lb) - (2/8 lb) = 1/8 lb.

So Karol used 1/8 lb of sugar for the cookies.