CA Foundation · Quantitative Aptitude · Measures of Central Tendency and Dispersion
In a class of 50 students, the mean marks of the boys is 60 and of the girls is 70. If the overall mean is 66, how many boys are in the class?
There are 20 boys. Setting 60b + 70(50 − b) equal to the total marks 66 × 50 = 3300 gives b = 20. Option 30 is the number of girls, so it is wrong.
- A20Correct
- B30
- C25
- D40
Explanation
Let boys = b. Then 60b + 70(50 − b) = 66 × 50 = 3300. So 3500 − 10b = 3300, giving b = 20. Check: 20×60 + 30×70 = 1200 + 2100 = 3300. The option 30 is the number of girls.
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