If  $$ \ {xy\over x+y}= a, $$ $${xz\over x+z}=b $$ and $$ {yz\over y+z} =c $$  where a, b, c are all non – zero numbers, then x equals to

Ratio of age of father, mother and son is 9:8:3. Five years hence sum of their age will be 95 years. Find the age of son 5 years ago.

A train is traveling at the rate of 45km/ hr. How many seconds will take to cover a distance of $$ {4\over5} $$ km? 

The reduction of Rs . 12 in the selling price of an article will changes 5 % gain into  $$ 2{1\over 2}\% $$ loss . The cost price of the article is 

A racing car going at an average speed of 108 km/ hr takes 15 minutes to complete a lap on a racing track. By how much should it increase its speed (in km/hr) to complete the lap in 12 minutes?

In an election between two candidates, 75% of the voters cast their votes, out of which 2% votes were declared invalid. A candidate got 9261 votes which were 75% of the valid votes. The total number of voters enrolled in that election was:

If a : b = 7 : 9 and b : c = 5 : 7, then what is a : c ?