If 16 toys cost 240, then what do 40 toys cost ?  Choose the correct choice from the following options:
A) Rs. 600	B) Rs. 620	C) Rs. 640	D) Rs. 660	E) None of these
Explanation:   Although we can first calculate the cost of one toy and then can multiply it with 40 to get the result.   but we will solve it with chain rule so that we can prepare ourself for other complex problems which we can solve easily by applying this rule.   Let the required cost be Rs. x   More toys means More Cost. (Direct Proportion)   15:40::240:x=&gt;x=240∗40/15=&gt;x=640   So 40 toys will cost Rs 640   Option Rs. 640
<result>C</result>
If 16 toys cost 240, then what do 40 toys cost ?