65 pupils from Class D and Class E took a Mathematics test. The average marks of the pupils was 85 marks. The average marks of the pupils in Class D was 92 marks and the average marks of the pupils in Class E was 79 marks. How many pupils were there in Class D?
Pupils in
Class D |
Total scores in
Class D |
Pupils in
Class E |
Total scores in
Class E |
Total scores of
Class D and Class E |
65
|
65 x 92 =
5980 |
0
|
0
|
5980
|
64
|
64 x 92 =
5888 |
1
|
1 x 79 =
79 |
5967
|
30
|
30 x 92 =
2760 |
35
|
35 x 79 =
2765 |
5525
|
Total scores of Class E and Class D
= 65 x 85
= 5525
If all the pupils are in Class D,
total scores
= 65 x 92
= 5980
Big difference
= 5980 - 5525
= 455
Small difference
= 92 - 79
= 13
Number of pupils in Class E
= 455 ÷ 13
= 35
Number of pupils in Class D
= 65 - 35
= 30
Answer(s): 30
