77 pupils from Class A and Class B took a Mathematics test. The average marks of the pupils was 82 marks. The average marks of the pupils in Class A was 86 marks and the average marks of the pupils in Class B was 72 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 |
77
|
77 x 86 =
6622 |
0
|
0
|
6622
|
76
|
76 x 86 =
6536 |
1
|
1 x 72 =
72 |
6608
|
55
|
55 x 86 =
4730 |
22
|
22 x 72 =
1584 |
6314
|
Total scores of Class B and Class A
= 77 x 82
= 6314
If all the pupils are in Class A,
total scores
= 77 x 86
= 6622
Big difference
= 6622 - 6314
= 308
Small difference
= 86 - 72
= 14
Number of pupils in Class B
= 308 ÷ 14
= 22
Number of pupils in Class A
= 77 - 22
= 55
Answer(s): 55
