The average of 15 numbers is 7. If the average of the first 8 numbers is 6.5 and the average of the last 8 number is 8.5. then middle number is

• 10

• 23

• 13

• 15

The average of 100 observations was calculated as 35. It was found later, that one of the observations was misread as 83 instead of 53. The correct average is

• 32.7

• 34.7

• 35.7

• 36.7

A man spends in 8 months as much as he earns in 6 months. He saves â‚¹ 6,000/- in a year. His average monthly income is:

• ₹ 2,400/-

• ₹ 2,000/-

• ₹ 2,150/-

• ₹ 1,800/-

The average age of a class of 39 students is 15 years. If the age of the teacher is included, then the average increases by 3 months. Find the age of the teacher.

• 30

• 25

• 35

• 40

The average age of 36 students in a group is 14 years. When the teacher's age is included in it, the average increases by one. The teacher's age in years is

• 31 years

• 51 years

• 36 years

• 50 years

A motor cycle gives an average of 45 km per litre. If the cost of petrol is Rs. 20 per litre. The amount required to complete journey of 540 km is (in Rs):

• Rs. 120/-

• Rs. 360/-

• Rs. 200/-

• Rs. 240/-

Number of boys and girls are 'x' and 'y' respectively; ages of a girl and a boy are 'a' years and 'b' years respectively. The average age (in years) of all boys and girls is

The average of 100 items was found to be 30. If at the time of calculation, two items were wrongly taken as 32 and 12 instead of 23 and 11, then the correct average is

• 29.8

• 29

• 29.9

• 29.5

89.

A box weighs 8.5 kg when full of sand and weighs 5.5 kg when it is half filled with sand. Weight of the empty box is

• 5 kg

• 6 kg

• 2.5 kg

• 4.5 kg

If the average age of four children is 12 years and the average age of these children and their fathers is 20 years, what is the age of the father?

• 52 years

• 48 years

• 62 years

• 54 years