Question

Mean of 100 items is 49. It was discovered that three items which should have been 60, 70, 80 were wrongly read as 40, 20, 50 respectively. The correct mean is

• A. 48
• B. $82\frac{1}{2}$
• C. 50
• D. 80

Answer 1

Answer: (C)

50

Answer 2

Sum of 100 items $= 49 \times 100 = 4900$

Sum of items added$= 60 + 70 + 80 = 210$

Sum of items replaced$= 40 + 20 + 50 = 110$

New sum $= 4900 + 210 - 110 = 5000$

∴ Correct mean$= \frac{5000}{100} = 50$.