Question

Five students wrote a mathematics test. The average mark was 68. If the marks for four of the students were 75, 62, 84 and 53, the mark of the fifth student was

Answer 1

66

Explanation:

Use the formula for the mean of a set of numbers:

sum of the numbers

average = --------------------------------

count of numbers

Here we know that the average mark was 68, so we can write:

75 + 62 + 84 + 53 + x

average = 68 = ----------------------------------

5

or 274 + x

68 = -------------------

5

Solving for x, we multiply both sides by 5: 340 = 274 + x.

Subtracting 274 from both sides effectively isolates x:

340 = 274 + x

- 274 -274

------------------------

66 = x

The fifth student's mark was 66.