Due to an increase of 30% in the price of eggs, 3 eggs less are available for Rs. 7.80. The present rate of eggs per dozen is?

Let the original rate be 'P' paise per egg.
Number of eggs bought for Rs. 7.80 = 780/P
New rate = (130% of P) paise per egg = 13P/10 paise per egg
Number of eggs bought for Rs. 7.80 = 780 x 10/13P = 600/P
∵ 780/P - 600/P = 3
⇒ 3P = 180
⇒ P = 60
So, present rate = (13 x 60)/10 paise per egg = 78 paise per egg
= Rs. 9.36 per dozen