Medium
A student scored 72, 68, x and 80 marks in four tests. If the mean marks of the four tests is 75, find the value of x.
Explanation
Explanation
Step 1: Mean = (sum of observations) ÷ (number of observations), so the sum = mean × number = 75 × 4 = 300.
Step 2: Add the known marks: 72 + 68 + 80 = 220.
Step 3: x = 300 − 220 = 80.
Step 4: Check: (72 + 68 + 80 + 80) ÷ 4 = 300 ÷ 4 = 75 ✓.
Answer: x = 80.
PRO TIP
Re-check your working by substituting the answer back into the original question.