From the notebook
Best Buy Questions: Use a Unit Rate, Not a Guess
Suppose one cereal box costs ₹156 for 650 g and another costs ₹185 for 800 g. Compare the cost per 100 g.
156 ÷ 650 × 100 = 24
The first box costs ₹24 per 100 g.
185 ÷ 800 × 100 = 23.125
The second box costs about ₹23.13 per 100 g, so it is the better buy.
Why unit rate helps
The pack sizes are different, so the sticker price alone is misleading. A unit rate puts both options onto the same scale.
Quick check: keep the same unit for every option: per item, per 100 g, per litre, and so on.
Useful next step: cover the worked answer and try the same method on a similar question before moving on.