80 pupils from Class A and Class B took a Mathematics test. The average marks of the pupils was 81 marks. The average marks of the pupils in Class A was 84 marks and the average marks of the pupils in Class B was 74 marks. How many pupils were there in Class A?
Pupils in
Class A |
Total scores in
Class A |
Pupils in
Class B |
Total scores in
Class B |
Total scores of
Class A and Class B |
80
|
80 x 84 =
6720 |
0
|
0
|
6720
|
79
|
79 x 84 =
6636 |
1
|
1 x 74 =
74 |
6710
|
56
|
56 x 84 =
4704 |
24
|
24 x 74 =
1776 |
6480
|
Total scores of Class B and Class A
= 80 x 81
= 6480
If all the pupils are in Class A,
total scores
= 80 x 84
= 6720
Big difference
= 6720 - 6480
= 240
Small difference
= 84 - 74
= 10
Number of pupils in Class B
= 240 ÷ 10
= 24
Number of pupils in Class A
= 80 - 24
= 56
Answer(s): 56
