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CBSE Class 7 · Mathematics

Large Numbers Around Us

Official NCERT chapter from Ganita Prakash Part I (book code gegp1). ExamMaster notes are original teaching at CBSE Class 7 depth.

This lesson follows the official chapter “Large Numbers Around Us” in Ganita Prakash Part I. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 7
  • Easy level
  • 8 concepts

1A Lakh Varieties!

A lakh is 100 thousands. 1,00,000 in the Indian grouping. “Many” is not a lakh until you can write the houses.

A lakh of names on a poster is a story; the number is 1 followed by five zeros in the Indian read.

Figure. One lakh is the digit 1 sitting in the lakh house, written 1,00,000 in the Indian grouping. The five zeros hold the lower houses open. They are not spare marks.

How it works

  1. Write 1 lakh in digits1,00,000.
  2. See five zeros after 1 in the Indian groupingHouses.
  3. Refuse “lots” as a lakhNeed the write.

2Land of Tens

Tens pile into hundreds, thousands, ten-thousands, lakhs. Each new house is ten of the last.

Skipping a house slides every digit — 10000 is not 1000.

Figure. In 45 the digit 4 is in the tens house, so it names 40. Swap the digits and the same marks become 54. The house, not the ink, is the number.

How it works

  1. Name the house you are inTens, hundreds, thousands…
  2. Ten of that house make the nextThe land of tens.
  3. Write zeros to hold empty housesDo not drop a house.

3Of Crores and Crores!

A crore is 100 lakhs: 1,00,00,000. Crores sit two houses left of lakhs in the Indian grouping.

Saying “crores” for a lakh is a house-slide.

Figure. A crore is 100 lakhs, written 1,00,00,000. On a decade scale a thousand, a lakh, and a crore sit two decades apart each, so none of them collapses to a speck.

How it works

  1. Write 1 crore1,00,00,000.
  2. See it as 100 lakhsThe trade.
  3. Keep lakh and crore as different housesNot synonyms.

100 lakhs

How many lakhs make 2 crores?

  • 1 crore100 lakhs
  • 2 crores200 lakhs
  • Digits2,00,00,000

Pro tip. Crore is a hundred-lakh bundle, not a new kind of digit.

4Exact and Approximate Values

Exact is the number you counted or were given. Approximate is a nearby round you name: to the nearest thousand, or “about 3 lakh”.

An approximate without a named rounding is a shrug.

Figure. 47,832 is the exact count. On a line from 47,000 to 48,000 it sits 832 of 1,000 of the way along, so the nearest thousand is 48,000. The mark is exact; the rounded name is approximate.

How it works

  1. Write the exact if you have itThe given.
  2. Name the roundingNearest thousand, or nearest lakh.
  3. Write the nearby numberAbout — with a method.

5Patterns in Products

Products of tens show a zero-count: 20 × 300 = 6000. Count the zeros after the non-zero multiply, then check a house.

20 × 30 is not 60 — you dropped a zero.

Figure. The product pattern climbs then falls: 11 × 11 is 121, and 111 × 111 is 12321. The unit is that mountain of digits, not a guess at the next mark.

How it works

  1. Multiply the non-zero fronts2 × 3 = 6.
  2. Count the zeros you still oweTwo zeros from 20 and 30? Check the houses.
  3. Write 600 and ask if a house is missing20×30=600.

6Did You Ever Wonder…?

Wonder here is a question you can put on a large number: how many thousands in 2 lakh? The wonder ends in a write, not a poem.

Wondering without a house-test is a poster.

Figure. Large numbers earn their houses by size. A year of days, a school of a thousand, a town of a lakh, and a crore sit on different decades. Wondering which house a count needs is the point.

How it works

  1. Ask a house-questionHow many thousands in this lakh-count?
  2. Write the trade1 lakh = 100 thousands.
  3. Answer in a numberThe wonder earned a record.

7A definition is a test you can run

“Lakh” and “crore” are tests: can you write them and trade them for thousands? A definition you cannot run is a label.

Memorising the words without a write is not this chapter.

Figure. A lakh is a test, not a pretty comma. 1,00,000 has the 1 in the lakh house and passes. 10,000 is ten thousand and fails the same test.

How it works

  1. Hear lakh or croreA name.
  2. Write the digits and the tradeThe test.
  3. If you cannot write it, you do not yet have the definitionRun it.

8Name the given before the unknown

The given is the number in the problem. The unknown is what it asks — thousands in a crore, or an approximate. Name the given first.

Hunting the unknown before reading the given is a scramble.

Figure. Name the given houses before asking the number. In 2,07,05,419 the 2 is crores, 07 is lakhs, 05 is thousands, and 419 is the rest. The commas are house marks, not decoration.

How it works

  1. Underline the given numberThis crore, this lakh.
  2. Name what is askedThe unknown.
  3. Trade houses only after both are namedGiven first.
1 crore in lakhs is
  1. 100 lakhs
  2. 10 lakhs
  3. 1000 lakhs

A crore is 100 lakhs.

Notes

  • The official chapter title is “Large Numbers Around Us”. Teach the school test for that title, not a contest shortcut.
  • If a step needs a later class, stop. The next official chapter will pick it up.

Formulas

  • 1 lakh = 1,00,000 = 100 thousands
  • 1 crore = 1,00,00,000 = 100 lakhs

Recap

Hold these pegs from the official chapter “Large Numbers Around Us”. The wording is ExamMaster’s teaching, not a textbook recap.

A Lakh Varieties!
A lakh is 100 thousands. 1,00,000 in the Indian grouping. “Many” is not a lakh until you can write the houses.
Land of Tens
Tens pile into hundreds, thousands, ten-thousands, lakhs.
Of Crores and Crores!
A crore is 100 lakhs: 1,00,00,000. Crores sit two houses left of lakhs in the Indian grouping.
Exact and Approximate Values
Exact is the number you counted or were given.
Patterns in Products
Products of tens show a zero-count: 20 × 300 = 6000.
Did You Ever Wonder…?
Wonder here is a question you can put on a large number: how many thousands in 2 lakh? The wonder ends in a write, not a poem.

Practise Large Numbers Around Us

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