A man can row 30 km downstream and return in a total of 8 hours. If the speed of the boat in still water is four times the speed of the current, then the speed of the current is: 

In what time will the simple interest be 2/5 of the principal at 8 percent per annum? 

A, B and C enter into a partnership. A invests Rs. 8000 for the whole year, B puts in Rs. 12000 at the first and increasing to Rs. 16000 at the end of 4 months, whilst C puts in at first Rs. 16000 but withdraw Rs. 4000 at the end of 9 months. Find the profit of A at the end of year, if the total profit is Rs. 22600.

A cloth merchant sold half of his cloth at a 40% profit. half of remaining at 40% loss and the rest was sold at the cost price. In the total transaction, his gain or loss will be

What approximate value should come in place of the question mark (?) in the following question? 
21.9714 × (8.8749 - 4.9393) = ?

Sides of a triangle are 13 cm, 84 cm and 85 cm. Find its area(in square cm)?

If the circumference of a circle increases from 4π to 8π, what change occurs in its area?