Question

John bought 100 eggs for rupees 40 out of these 4 were found to be broken and he sold the remaining eggs @ rupees 7.50 per dozen find his gain or loss percent

Answer 1

price one egg is 40/100 = 0.4 rupees 

when 4 were found broken then remaining eggs = 100-4=96 eggs 

96 eggs =96/12 =8 dozens

selling price of remaining eggs = 7.50  * 8

selling price of remaining eggs =60 rupees

then 

he get the profit of 20 rupees

percent = 20*100/40 

profit percentage = 50%

i hope this is right and will help you

Answer 2

No. Of egg bought by john=100
Total rupees he pay for 100eggs =40
Therefore rupees for, 1 egg=40/100=0.4
That is he bought 0.4rupees /egg
4eggs are broken therefore remaining eggs=100-4=96eggs
1 dozen = 12
96/12=8 dozen eggs he have
Cost for 1 dozen = 7.5
Cost for 8 dozen= 7.5*8=60
Gain = selling price - cost price
=60-40=20
Gain%=profit *100%toal price
=20*100/40=50%