The average marks of Naveen decreased by one when he replaced the subject in which he has scored 40 ...........

Quantitative Aptitude ( CCS) Average

The average marks of Naveen decreased by one, when he replaced the subject in which he has scored 40 marks by the other two subjects in which he has scored 23 and 25 marks respectively. Later he has also included 57 marks of Maths, then the average marks increased by two. How many subjects were there initially?

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Explanation:

Solution:
Total subjects = x ; Average Marks = y
(x + 1)(y – 1) = (xy – 40) + (23 + 25)
y – x = 9 –(1)
(x + 2)(y + 1) = (xy – 40) + (23 + 25)+ 57
xy + 2y + x + 2 = xy + 65
2y + x = 63 –(2)
From Equation (1) and (2) => x = 15.