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Class 7 Large Numbers Around Us: cheat sheet
CBSE Mathematics. Reading and writing large numbers in the Indian system (lakhs, crores) and the international system (millions, billions), and rounding and estimating them.
Key ideas
- Indian commas: the first comma after 3 digits from the right, then after every 2 digits: 4,56,78,912.
- International commas: after every 3 digits from the right: 45,678,912.
- Read a number group by group, naming each group: 4,56,78,912 is four crore fifty-six lakh seventy-eight thousand nine hundred twelve.
- Rounding to a place: look at the next digit; 5 or more rounds up, less than 5 rounds down.
- Estimate by rounding each number first, then work out the rough answer.
Remember
| Indian | 1 lakh = 1,00,000; 1 crore = 1,00,00,000 = 100 lakh |
| International | 1 million = 1,000,000; 1 billion = 1,000,000,000 |
| Between the systems | 10 lakh = 1 million; 1 crore = 10 million; 100 crore = 1 billion |
Watch out
- Putting Indian commas every 3 digits.
- Reading 1 crore as 1 million (it is 10 million).
- Rounding by looking at the wrong digit.
Worked example
Write 916751036 with commas in the Indian system and in the international system.
Working: Indian: 3 digits, then groups of 2; international: groups of 3
Answer: Indian 91,67,51,036; international 916,751,036
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