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SSC CHSL 2022 PYQ — Question 53

SSC CHSL - 26 May 2022 - Shift 2 • Quantitative Aptitude • Q53

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If the average marks of three classes of 30, 50, and 70 students are 55, 70, and 70 respectively, then the average marks of all the students are: 

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Correct answer: A

Explanation

The correct answer is Option 1 i.e. 67.

We know that,

Average = Sum of observations/Number of observations

Now,

Average marks of 30 students = 55

So, the total marks of 30 students = 30 × 55 = 1,650

Average marks of 50 students = 70

So, the total marks of 50 students = 70 × 50 = 3,500

Average marks of 70 students = 70

So, the total marks of 70 students = 70 × 70 = 4,900

Now,

The total number of students = (30 + 50 + 70) = 150

And the total marks = (1,650 + 3,500 + 4,900) = 10,050

So, the required average = Total marks/Total students

Required average = 10,050/150 = 67