Question

A data set consists of $6$ (not distinct) positive integers: $1,$ $7,$ $5,$ $2,$ $5,$ and $X.$ The average (arithmetic mean) of the $6$ numbers equals a value in the data set. What is the sum of all positive values of $X?$

$10$

$26$

$32$

$36$

$40$

Answer: D

Concepts:mean casework

Difficulty rating: 1070

Solution:

The average of the $6$ numbers is $\dfrac{1 + 7 + \cdots + X}{6} = \dfrac{20 + X}{6}.$

This value can equal any of the terms in the set, so we can case on what it equals.

$\dfrac{20 + X}{6} = 1 \iff X = -14$

$\dfrac{20 + X}{6} = 7 \iff X = 22$

$\dfrac{20 + X}{6} = 5 \iff X = 10$

$\dfrac{20 + X}{6} = 2 \iff X = -8$

$\dfrac{20 + X}{6} = X \iff X = 4$

Adding up all the positive values for $X,$ we get $36.$

Thus, D is the correct answer.

2022 AMC 10A Problem 8

Answer: D

Difficulty rating: 1070

Solution:

Problem 8 in Other Years