54 pupils from Class C and Class D took a Mathematics test. The average marks of the pupils was 78 marks. The average marks of the pupils in Class C was 84 marks and the average marks of the pupils in Class D was 75 marks. How many pupils were there in Class C?
Pupils in
Class C |
Total scores in
Class C |
Pupils in
Class D |
Total scores in
Class D |
Total scores of
Class C and Class D |
54
|
54 x 84 =
4536 |
0
|
0
|
4536
|
53
|
53 x 84 =
4452 |
1
|
1 x 75 =
75 |
4527
|
18
|
18 x 84 =
1512 |
36
|
36 x 75 =
2700 |
4212
|
Total scores of Class D and Class C
= 54 x 78
= 4212
If all the pupils are in Class C,
total scores
= 54 x 84
= 4536
Big difference
= 4536 - 4212
= 324
Small difference
= 84 - 75
= 9
Number of pupils in Class D
= 324 ÷ 9
= 36
Number of pupils in Class C
= 54 - 36
= 18
Answer(s): 18
