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Answers
WE FIND CLASS MARK xi fixi ∑fi=100
63+x+y=100
x+y=100-63
x+y=37 (1)
5 35
15 150
25 25x
35 455
45 45y
55 550
65 910
75 675
total=2775+25x+45y
mean=∑fixi/∑fi
mean is given as 42
42=2775+25x+45y/100
42*100=2775+25x+45y
4200-2775=25x+45y
1425=25x+45y- (2)
37=x+y (1)
1425=25x+45y
925=25x+25y
- - -
500=20y
y=500/20
y=25
put y=25 in eq 1
x+y=37
x+25=37
x=37-25
x=12