75 pupils from Class K and Class L took a Mathematics test. The average marks of the pupils was 85 marks. The average marks of the pupils in Class K was 87 marks and the average marks of the pupils in Class L was 81 marks. How many pupils were there in Class K?
Pupils in
Class K |
Total scores in
Class K |
Pupils in
Class L |
Total scores in
Class L |
Total scores of
Class K and Class L |
75
|
75 x 87 =
6525 |
0
|
0
|
6525
|
74
|
74 x 87 =
6438 |
1
|
1 x 81 =
81 |
6519
|
50
|
50 x 87 =
4350 |
25
|
25 x 81 =
2025 |
6375
|
Total scores of Class L and Class K
= 75 x 85
= 6375
If all the pupils are in Class K,
total scores
= 75 x 87
= 6525
Big difference
= 6525 - 6375
= 150
Small difference
= 87 - 81
= 6
Number of pupils in Class L
= 150 ÷ 6
= 25
Number of pupils in Class K
= 75 - 25
= 50
Answer(s): 50
