50 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 93 marks and the average marks of the pupils in Class B was 78 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 |
50
|
50 x 93 =
4650 |
0
|
0
|
4650
|
49
|
49 x 93 =
4557 |
1
|
1 x 78 =
78 |
4635
|
10
|
10 x 93 =
930 |
40
|
40 x 78 =
3120 |
4050
|
Total scores of Class B and Class A
= 50 x 81
= 4050
If all the pupils are in Class A,
total scores
= 50 x 93
= 4650
Big difference
= 4650 - 4050
= 600
Small difference
= 93 - 78
= 15
Number of pupils in Class B
= 600 ÷ 15
= 40
Number of pupils in Class A
= 50 - 40
= 10
Answer(s): 10
