A recipe that serves 6 uses 1 1/2 cups of flour. How many cups are needed to serve 15?

Answer 1

1 1/2 = 3/2

3/2 divided by 6 = 3/12 = X divided by 15

3/12 = X/15

divide denominators by 3

3/4 = X/5

cross multiply

4X = 15

X = 15/4 = 3 3/4 cups to serve 15

1 1/2 served 6, double that and

3 cups serves 12

you want 15, another 3 people, so add half of 1 1/2 = half of 3/2 = 3/4

3 3/4 cups serves 15