Given cost of one dozen eggs = Rs. 6.40
Cost of 50 dozen eggs = 50 x 6.40 = Rs. 320
Total number of eggs = 50 x 12 = 600
Number of eggs left after removing the broken ones = 600 – 20 = 580
SP of 1 egg = 55 paise
So, SP of 580 eggs = 580 x 55 = 31900 paise
= Rs. 31900/100
= Rs. 319
Loss = CP – SP
= Rs. (320 – 319) = Rs. 1
Loss % = (Loss/CP) x 100
= (1/320) x 100
Loss = 0.31%