SOLUTION: Sarah needs to make a cake and some cookies. The cake requires 3/8 cup of sugar and the cookies require 3/5 cup of sugar. Sarah has 15/16 cups of sugar. Does she have enough sugar,

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Question 252641: Sarah needs to make a cake and some cookies. The cake requires 3/8 cup of sugar and the cookies require 3/5 cup of sugar. Sarah has 15/16 cups of sugar. Does she have enough sugar, or how much more does she need?
Found 2 solutions by jim_thompson5910, richwmiller:
Answer by jim_thompson5910(35256) (Show Source):
You can put this solution on YOUR website!
Simply add the two fractions and to get:

So she'll need cups of sugar. Now the question is: which fraction is larger, or ?

To answer this question, first assume that they are equal:

Cross multiply

Multiply

Now change the equal sign '=' to a less than sign '<' (since 600 is less than 624).

Because the left side is less than the right, this means that the left side of is smaller than the right. So change the '=' to a '<' to get

Since is smaller than , this means that she has less sugar than what she needs. So she does NOT have enough sugar.

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How much does she need then? Well let's figure that out.

To find that out, just subtract the amount she has () from the amount she needs () to get:

So she needs of a cup of sugar.

Answer by richwmiller(17219) (Show Source):
You can put this solution on YOUR website!
We have several fractions with various denominators.
We need to add 3/8 and 3/5 to see if the sum is less than or equal to 15/16
5*8=40 but 16 is not a factor of 40
5, 8 and 16 are all factors of 80
So we multiply 3/8 by 10/10 and get 30/80
3/5 by 16/16 and get 48/80
15/16 by 5/5 and get 75/80
So now we add 48/80 and 30/80 and get 78/80 and see that it is more than 75/80
So technically there is not enough sugar but recipes are not usually that strict.
She needs 3/80 cups of sugar