Question

The average of 13 papers is 40. The average of the first 7 papers is 42 and of the last seven papers is 35. Find the marks obtained in the 7th paper.

Answer 1

check it..........................

Answer 2

The mark scored in 7th  paper is 19  

Given:

The average of 13 papers is 40. The average of the first 7 papers is 42  and of the last seven papers is 35.  

To find:

Marks scored in the 7th paper  

Solution:

(i) The average of 13 papers is 40

We know that average $=\frac{\text {total marks obtained}}{\text {number of papers}}$

$40=\frac{\text { Total marks obtained}}{13}$

Thus, total marks obtained $=40 \times 13 = 520\ \text{marks}$

(ii) Now, the average of first 7 papers is 42

We know that average $=\frac{\text {total marks obtained}}{\text {number of papers}}$

Hence, 42 $=\frac{\text {Totalmarks obtained in last 7papers}}{7}$

Thus, total marks obtained in first 7 papers $=42 \times 7=294\ \text{marks}$

(iii) The average of last 7 papers is 35

Hence, $35 = \frac{\text { Total marks obtained in last } 7 \text { papers }}{7}$

Thus, total marks obtained in last 7 papers $=35 \times 7= 245$ marks

(iv) Total of 13 paper + 7th paper = 294 + 245 = 539  

Therefore, we can say that 520 + 7th paper = 539

Hence, 7th paper = 539 - 520 = 19 marks.