35 is the average marks obtained by 120 students. The average marks of successful candidates was 39 and that of unsuccessful candidates was 15. What is the number of successful candidates in that examination ?
Let there be x successful candidates in the exam.
Unsuccessful candidates = 120 - x
Total score = 35 x 120
Total score is also equal to x * 39 + (120 - x) * 15
So, x = (35 * 120 - 120 * 15)/ 24 = 120 * 20 / 24 = 100
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