How many bricks, each measuring 25 cm x 11.25 cm x 6 cm, will be needed to build a wall of 8 m x 6 m x 22.5 cm?

The average of 8 readings is 24.3, out of which the average of the first two is 18.5 and that of next three is 21.2. If the sixth reading is 3 less than seventh and 8 less than eight, what is the sixth reading? 

If a number is increased by 30 % and after that it is decreased by 25 % and again it is increased by 25 % then find average change in percentage? (approx.) 

Find the exact value of the following question:

The ratio between speed of boat in down stream and speed of stream is 9 : 1. If the speed of current is 3 km/hr, then find the distance travelled in upstream in 5 hours. 

The present age of a father is 3 years more than three times the age of his son. Three years hence, father's age will be 10 years more than twice the age of the son. The father's age is: 

The simple interest on an amount at the rate of 13.5 p.c.p.a. for 10 years is Rs. 765.45. What is the sum?

What is the value of