A vendor bought 40 dozen of fruits for ₹2400. Out of these, 30 fruits were rotten and thrown away. At whatrate per dozen should hesell the remaining fruits to make a profit of 25%?

we know 

cost price of 40 dozen fruit is 2400

and 1 dozen =  12 fruits 

i.e 40 dozen = $$12\times{40}$$ = 480

therefore cost of 1 fruit is 2400$$\div{480}$$ = 5

now

to get 25% as profit he must sell the fruits at rs 3000 

because 25% of 2400 

[$$25\div{100}]\times{2400}$$  = 600 

and selling price = profit gained + cost price

now if 30 fruits are rotten than the

total number of fruits remaining is 480-30=450 

so now he must sell the remaining fruits at rs 3000 to get 25% profit

remaining fruits to be sold = 450

selling price is 3000

if he sells 450 fruits in 3000 

than 1 fruits is sold at $$3000\div{450}$$

                                  = $$\frac{20}{3}$$

so 12 fruits is sold at $$\frac{20}{3}\times{12}$$

so he sells 12 fruits i.e one dozen fruits at 80 rupees