Multiple choice

The average marks of some students in a class is 43. When 4 students are included the average becomes 42.5 and the marks of those 4 students are 42, 36.5, 39 and 42.5 in the class. The number of students in the class was ?

  1. 15

  2. 20

  3. 25

  4. 35
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let n be original students. Total marks = 43n. Adding 4 students with marks 42+36.5+39+42.5 = 160 gives: (43n+160)/(n+4) = 42.5. Solving: 43n+160 = 42.5n+170, so 0.5n = 10, n = 20. So there were 20 students originally.

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