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?

$3$

$4$

$5$

$6$

$7$

Answer: C

Concepts:weighted mean bounding to limit cases mixture ratio and proportion

Difficulty rating: 1900

Solution:

Let there be $n$ people, drinking $8n$ ounces total, split into milk $M$ and coffee $C.$ Angela drank one cup, so $\tfrac14 M + \tfrac16 C = \tfrac1n (M + C).$

The left side is a weighted average of $\tfrac14$ and $\tfrac16,$ so $\tfrac1n$ lies strictly between $\tfrac16$ and $\tfrac14.$ That forces $4 \lt n \lt 6,$ so $n = 5.$

Thus, the correct answer is C.

2000 AMC 10 Problem 22

Answer: C

Difficulty rating: 1900

Solution:

Problem 22 in Other Years