How Babu Spotted the Clerk's Math Error

Simple Arithmetic Catches Overcharge

Price per kg: 4.29 babu
Quantity bought: 4 kg
Correct total: 4 × 4.29 = 17.16 babu

The clerk charged 19.96 babu, which is significantly higher. Babu knew the per-kg price and quantity, so he immediately recognized the discrepancy.