Question

One morning each member of Angela's family drank an $8$ -ounce mixture of coffee with milk. The amounts of coffee and milk varied from cup to cup, but were never zero. Angela drank a quarter of the total amount of milk and a sixth of the total amount of coffee. How many people are in the family?

$3$

$4$

$5$

$6$

$7$

Solution:

Measure amounts in $8$ -ounce cups, so Angela's cup holds $c$ coffee and $m$ milk with $c + m = 1.$

Since Angela drank a sixth of the coffee, the total coffee is $6c$ ; since she drank a quarter of the milk, the total milk is $4m.$ The number of people equals the total number of cups, $6c + 4m = 6c + 4(1 - c) = 4 + 2c.$

This is an integer only when $2c$ is an integer, and since $0 \lt c \lt 1$ this forces $c = \tfrac12,$ giving $4 + 1 = 5$ people.

Thus, the correct answer is C.

2000 AMC 12 Problem 13

Solution:

Problem 13 in Other Years