The average earning of a mechanic for the first-four days of a week is Rs. 18 and for the last four days is Rs. 22. If he earns Rs . 20 on the fourth day, his average earning for the whole week is?

Let third number = y
Then, second number = 2y
and first number =4y

? ( y + 2y + 4y) / 3 = 42
? 7y = 42 x 3
? y = 18

so, (largest) - (smallest) = ( 4y - y)
= 3y
=54

Let the present ages of father be 3x and daughter be x .
so the 4 year ago father's age and daughter's age was
( 3x - 4 ) and ( x - 4 )
? ( 3x - 4 / x -4 ) = 4 / 1
? x = 12 year and 3x = 36 year

Required average
= Old average - Sold average
= ( 250 ) - ( 10 ) = 240

Let the number of failed student = Y
? Number of passed student = 80 - Y

sum of marks of all students = sum of marks of passed students + sum of marks of failed students
80 x 40 = (80 - Y) x 60 + 35Y
? 3200 =4800 - 60Y + 35Y
? 25Y = 1600
? Y = 64
? Number of students who failed = 64

Let ages of Dinesh, Mahesh and Rahul be D, M and R, respectively.
Then,
D + M = 2 x 16 = 32 ...(i)
M + R = 2 x 13 = 26 ....(ii)
D + R = 2 x14 = 28 ....(iii)

On adding Eqs. (i), (ii) and (iii), we get
2(D + M + R) =86
? D + M + R = 43 ....(iv)

On subtracting Eqs. (iii) from Eq. (iv), we get
M = 43 - 28
? M = 15 Yr

Let the total number of workers be y.
So sum of salary for all workers = sum of salary of 7 technician + sum of salary for other y -7 workers.
7 x 1000 + 780(y -7) = 850 y
? 7000 + 780y - 5460 = 850y
? 70y = 1540
? y = 22

So total number of workers = 22

Weight increase = 8 x 2 kg = 16 kg
weight of new man= 50 + 16 = 66 kg

Weight of the teacher = Total weight of 40 students and teacher - total weight of 40 students
= 41 x 40.5 - 40 x 40 kg
= 60.5kg

New average = 120% of old average
=120% of 18.5
= (120 x 18.5) / 100
= 22.2

Age of coach = Total weight of 4 players and coach - total weight of 4 players
= 5 x 22.2 - 4 x 18.5
= 37 years

Let the age of youngest child be y.
so from question y + (y + 4) + (y + 8) + (y + 12) = 4 x 12
? 4y + 24= 48
? y = 6 years