Answer:
12 cups
Step-by-step explanation:
The ratio he uses is
2 parts strong coffee
3 parts milk
Let's say he makes a recipe exactly like the amounts of the ratio.
2 cups strong coffee
3 cups milk
Total: 2 cups + 3 cups = 5 cups
He wants to make 30 cups, so 5 cups is not enough.
Let's double the amounts of the recipe keeping the same ratio of 2 to 3.
2 × 2 = 4 cups strong coffee
3 × 2 = 6 cups milk
Total: 4 cups + 6 cups = 10 cups
He wants to make 30 cups, so 10 cups is not enough.
We can keep on going up by multiplying the numbers in the ratio by larger numbers, but there is a quicker way.
We need to multiply both numbers in the ratio by a number, let's call it x, so that when both numbers in the ratio are multiplled by x, and the ingredients are added, we end up with 30 cups.
Multiply both numbers in the ratio by x.
2x cups of strong coffee
3x cups of milk
Now add: the total amount will be 5x cups
We want 30 cups, so
5x = 30
Solve for x.
x = 30/5 = 6
x, the multiplier we need is 6.
2x cups strong coffee = 2(6) cups = 12 cups
3x cups milk = 3(6) cups = 18 cups
Answer: 12 cups
