Decimals and place value

Story hook

Imagine you walk into a little shop with 10 rupees in your hand. You ask for a toffee. The shopkeeper says, "That's 1 rupee and 50 paise." You hand over a 10-rupee note. He gives you back a 5-rupee coin, a 2-rupee coin, a 1-rupee coin, and one 50-paise coin.

Did he cheat you? Let's see. You gave 10. The toffee cost 1 rupee 50 paise, which we write as ₹1.50. So you should get back ₹8.50. The coins he gave: 5 + 2 + 1 = ₹8, plus 50 paise = ₹8.50. He was honest!

That little dot in ₹1.50 and ₹8.50 is the star of today's lesson. It is called the decimal point. It is the tiny dot that separates the whole rupees from the paise — the full things from the small leftover bits.

By the end of this lesson, you will read, write, compare, add, subtract and multiply numbers with that dot — and you'll turn fractions like 3/4 into 0.75 in your head. No fear. Just one small idea, repeated.

Why this matters for UPSC

CSAT is Paper II of the UPSC Prelims. It is a qualifying paper — you only need 33% to pass. You do NOT need to be a genius. You just need to be quick and not make silly mistakes.

Decimals show up everywhere in CSAT:

• Averages of marks come out as decimals (like 67.5).
• Money sums (profit, discount, simple interest) use rupees and paise.
• Measurement questions use 2.5 metres, 1.75 litres, 0.5 kg.
• Data tables (graphs and charts) are full of decimal values.

Get decimals right and you grab easy, fast marks — the kind that push you safely over 33%.

And in real life? Every time you check a shop bill, split a restaurant cheque, read your phone's battery percentage, or measure cloth for a shirt — you are using decimals. This lesson is as much for your daily life as for the exam.