Direction : What value should come in place question mark(?) in the following questions?

$$2\over7$$ of $$ 5\over6$$ of ?=200

A wholesaler purchased 7 hair clips for a rupee. How many for a rupee must he sell to get profit of 40%?

A librarian purchased 60 story books for his library. But he found that he could get 4 extra books by spending Rs. 336 more and then the overall average price per book would be reduced by Re 1. The previous average price of each book was 

The selling price of the product was equal to 50% of its cost price. Two gradual discounts were offered on the product. If the first discount was 20%, then what was the second discount?

A train travelling at 48 km/hr crosses an another train half of its length and travelling in opposite direction at 42 km/hr in 12 seconds. It also passes a railway platform in 45 seconds. The length of the railway platform Is

If $$ x={\sqrt3\over{2}}$$ then the value of $$ \sqrt{1+x}-\sqrt{1-x}$$ will be

A started the business with the investment of Rs. 36000. B and C joined him with some investments after 3 and 6 months. The profit is divided in the ratio of 2 ∶ 3 ∶ 5 at the end of the year. Find the difference between the investment made by B and C in the business.

The radius of circle is increased by 1%. How much does the area of the circle increased?