Large Numbers Around Us — Class 7 Mathematics
Ganita Prakash Part 1 · Chapter 1
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Chapter summary
This chapter builds a feel for very large numbers — lakhs, crores and arabs — and connects them to millions and billions. You learn that lakh is followed by five zeroes and crore is followed by seven zeroes . The Indian system groups digits in a comma pattern while the American (International) system groups them uniformly in threes, so million equals ten lakhs. You practise reading and writing numbers in both systems, comparing them, and finding "nearest neighbours" (nearest thousand, lakh, crore) by rounding up or rounding down. The chapter stresses that exact values are not always needed — a good estimate often communicates size better. Through thought experiments (Can Mumbai fit in one lakh buses? How many coins stack up to the Statue of Unity?) you sharpen estimation. You also explore multiplication shortcuts such as multiplying by being the same as dividing by and multiplying by , and spot patterns in the number of digits a product can have.
Reading and writing large numbersIndian vs American place value systemsExact and approximate values & roundingNearest neighbours and estimationPatterns in products and multiplication shortcuts
Key ideas & terms
- Lakh
- One lakh =
, written as 1 followed by five zeroes; equals one hundred thousand. - Crore
- One crore =
, written as 1 followed by seven zeroes; equals one hundred lakhs. - Indian place value system
- Digit grouping in a 3-2-2 pattern from the right (thousands, lakhs, crores).
- American / International system
- Digit grouping uniformly in threes (thousands, millions, billions).
- Rounding (up / down)
- Replacing a number by a nearby convenient value; rounding up gives more, rounding down gives less.
- Nearest neighbours
- The nearest thousand, ten thousand, lakh, ten lakh and crore to a given number.
- Estimation
- Finding an approximate value that is close enough for the purpose at hand.
Extra questions & answers
How many zeroes are there in one lakh?
Five zeroes — one lakh is written as
How many zeroes are there in one crore?
Seven zeroes — one crore is written as
How many lakhs make one crore?
One hundred lakhs make one crore
How is one million related to lakhs?
One million equals ten lakhs
How does the Indian system place commas in 1278830?
As
How much less than one lakh is 75000?
It is
How many thousands make one lakh?
One hundred thousands make one lakh.
Why is multiplying by 5 the same as dividing by 2 then multiplying by 10?
Because
What is the value of 1 arab?
One arab is
When should we round a large number instead of using its exact value?
When only the approximate size matters, e.g. saying a town has about 75,000 people instead of 76,068.

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