A student obtained 60,75 and 85 marks respectively in three monthly examinations in Mathematics and 95 marks in the final examination. The three monthly examinations are of equal weightage whereas the final examination is weighted twice as much as a monthly examination. The mean marks of Mathematics are
81
82
80
85
A
80
B
85
C
81
D
82
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Solution
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We have x1=60,x2=75,x3=85,x4=95,w1=1,w2=1,w3=1 and w4=2 ∴¯¯¯¯¯¯¯¯Xw=w1x1+w2x2+w3x3+w4x4w1+w2+w3+w4 ⇒¯¯¯¯¯¯¯¯Xw=1×60+1×75+1×85+2×951+1+1+2=4105=82
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