The speed of a boat downstream is 15 km/hr. and the speed of current is 3 km/hr. Find the total time taken by the boat to cover 15 km upstream and 15 km downstream. 

The ratio of the speeds of the two airplanes is 11: 18. If the first airplane covers a distance of 1650 km in 3 hours, then what is the speed (m / s) of the second airplane?

$$ {x+{1\over{x}}}$$, then the value of $$ {x^2}+{1\over{x^2}}$$ is

The average score obtained by Sandeep in 12 Tests is 25. Rumella has an average of 23 marks so far, but has competed in only 8 Tests. What average will Rumela have to earn in the remaining 4 Tests to be equal to Raghuveer's average?

Find the value of $$ {1\over{2×5}}+{1\over {5×8}}+{1\over {8 × 11}}+......{1\over {23 × 26}}=?$$

A man can row at a speed of $$4{1\over 2}$$km/hr in still water. If he takes 2 times as long to row a distance upstream as to row the same distance downstream, then the speed of stream (in km/hr) is : 

A tradesman marks his goods at 20 % above the cost price. He allows his customers a discount of 8% on marked price. Find out his profit percent.