3 chairs and 2 tables cost Rs. 700 and 5 chairs and 3 tables cost Rs. 1100. What is the cost of 1 chair and 2 tables?

Let say, 

cost of a chair is c and cost of a table is t.

So, from first condition,

$$3c+2t=700...............(1)$$

and from second condition,

$$5c+3t=1100..............(2)$$

Now,multiply equation (1) by 3 :

$$9c+6t=2100..........(4)$$

and multiply equation (2) by 2:

$$10c+6t=2200........(5)$$

Now,Subtract equation (5) and (4),

$$c=100.$$

Put c=100 in equation (1):

$$300+2t=700$$

or,$$2t=400$$

or,$$t=200.$$

So, cost of one chair and 2 table is 

$$100+2×200=500.$$

C is correct choice.