Question

Brigitte's average on her six math tests this marking period is 75. Fortunately for Brigitte, her teacher drops each student's lowest grade, and this raises Brigitte's average to 85. What was her lowest grade?

Answer 1

Brigitte's lowest mark was `25`

Explanation:

Let `S_H` be the sum of Brigitte's 5 highest marks.
`rarr S_H=5xx85 = 425`

Let `L` be Brigitte's lowest mark.
`rarr (S_H +L)/6=75`

Therefore
`color(white)("XXX") (425+L)/6=75`

`color(white)("XXX") rarr 425 +L =75xx6=450`

`color(white)("XXX") rarr L=450-425 =25`