The average age of a group of 10 friends is 15 yr. If one friend leaves the group, the average becomes 16 yr. Find the age of the friend who left the group.

sum of observations
= 308 + 142 + 160 245 + 25 = 880

Average = Sum of all observations / Number of observations
=880 / 5
=176

Age E = ( A + B + C + D + E ) - [ ( A + B ) + ( C + D ) ]
= ( 40 x 5 ) - [ ( 35 x 2 ) + ( 42 x 2 )]
=200 - ( 70 + 84)
= 200 - 154
= 46

Average speed =2 x 40 x 60 / ( 40+ 60)
= 4800 / 100
= 48 km/hr

No. of executives / No. of non- executives
= 2 / 1
Therefore
Number of executives = 40
and number of non executives employees = 20
now , go through the options
Total salary = 40 x salary of executives + 20 x salary of non-executives
60 x 12000 = 40 x k + 20 x l, here k, l are unknowns
so we con't determine the required average salary

Total income = Total expenditure + Total savings
We are not find the average savings of B and C, Since data is insufficient.

Average of first n natural numbers = ( n + 1 ) / 2
= ( 79 + 1 ) / 2
= 40

Average will increase by 8 times.
So average of new members = (21 x 8 ) = 168

Sum of 50 member = (50 x 38 )
= 1900

Sum of 48 member = [1900- (45 + 55 ) ]
= 1800

? Required Average = 1800/48
= 225/6
= 37.5

Let the average for last 4 matches be y.
Sum of score for 10 matches = sum of score for first 6 matches + sum of score of last 4 matches.
So 53 x 6 + 4y = 10 x 43.9
? 4x= 439-318
?4x= 121
? x= 30.25

Average height of the whole class = sum of height of 40 girls / 40
= (30 x 160 + 10 x 156) / 40
= 159 cms.