A shopkeeper sells eggs at 20 for a rupee gaining 30%. How many eggs did he buy for a rupee?

SP of 20 eggs = ₹ 1 and gain = 30%
CP of 20 eggs = (1 x 100)/130 = ₹ 10/13
Now, ₹ 10/13 yields 20 eggs.
∴ ₹ 1 will yield (20 x 13)/10 = 26 eggs
Clearly, 26 eggs were bought for ₹ 1.