# Abby scored a 78 on her first test and a 54 on her second. If Abby needs a test average of 55 to pass the course, what is the lowest score that she can make on her third and final test and still pass?

Nov 8, 2016

$55$

#### Explanation:

The lowest average of the 3 tests must be 55 in order for Abby to pass.

Let the lowest mark be $m$

$\frac{78 + 54 + m}{3} = 55 \text{ } \leftarrow \times 3$

$78 + 54 + m = 165$

$m = 165 - 78 - 54$

$m = 33$

The high mark in the first test means that she only needs 33 in the third test to have an average of $55$.