Question

Question #6640b

Answer 1

`"To make 90 cookies, you will need 6 cups of flour."`

Explanation:

There are a couple of good ways to solve this problem.

1) Solve by logic

It is given that     60 cookies need 4 cups of flour
That means that 30 cookies need 2 cups of flour
`color(white)(........................)`....................................
Therefore `color(white)(,.......)`90 cookies need 6 cups of flour `larr` answer

....................................................

2) Solve by math

Set up a series of ratios and solve for `f`, the number of cups of flour needed

`("cookies")/("flour") = (60)/(4) = (90)/ (f)`

NOTE: Always write a word fraction to keep your numbers organized.
The most common error is to write the numbers on the wrong side of the fraction bar.

1) Cross multiply
`(4)(90) = 60f`

2) Divide both sides by 10 to make those numbers smaller
`(4)(9) = 6f`

3) Clear the parentheses
`36 = 6f`

4) Divide both sides by `6` to isolate `f`, already defined as "the number of cups of flour needed
`6 = f` `larr` same answer

Answer:
To make 90 cookies, you will need 6 cups of flour.