69 pupils from Class N and Class P took a Mathematics test. The average marks of the pupils was 83 marks. The average marks of the pupils in Class N was 85 marks and the average marks of the pupils in Class P was 79 marks. How many pupils were there in Class N?
Pupils in
Class N |
Total scores in
Class N |
Pupils in
Class P |
Total scores in
Class P |
Total scores of
Class N and Class P |
69
|
69 x 85 =
5865 |
0
|
0
|
5865
|
68
|
68 x 85 =
5780 |
1
|
1 x 79 =
79 |
5859
|
46
|
46 x 85 =
3910 |
23
|
23 x 79 =
1817 |
5727
|
Total scores of Class P and Class N
= 69 x 83
= 5727
If all the pupils are in Class N,
total scores
= 69 x 85
= 5865
Big difference
= 5865 - 5727
= 138
Small difference
= 85 - 79
= 6
Number of pupils in Class P
= 138 ÷ 6
= 23
Number of pupils in Class N
= 69 - 23
= 46
Answer(s): 46
