A milk packet is priced at ₹7.50, and the booth takes 45 paise extra for a carry bag. The carry-bag amount is what per cent of the price of the milk packet?

Bring both amounts to the same unit: ₹7.50 = 750 paise. Then 45/750 = 0.06 = 6%. 60% comes from reading ₹7.50 as 75 paise - the decimal point moved one place. 600% divides 45 paise straight by ₹7.50 without converting at all, mixing paise with rupees. 0.6% is a slipped decimal in the other direction. Always convert first; a percentage only means something when both quantities are in the same unit.