Track quiz

Ten ideas, ten checks. The table sits first, so there is somewhere to look back.

Ten moves for a number too long to take in at a glance
Move	How it goes
Name the column	Thousand, ten thousand, lakh, ten lakh, crore. Each is ten of the one before.
Place the commas	Indian: after 3 digits, then twos. International: threes all the way.
Read it out	Label each Indian group crore, lakh, thousand. Skip a group of zeros.
Compare two	More digits wins. On a tie, walk left and stop at the first difference.
Round it	Half that place or more goes up. Less than half goes down.
Estimate first	Round both, multiply, and keep answers between half and double.
Feel the size	A lakh is ten pages of 10,000 dots. A crore is a hundred lakh.
Round which way	Round up when you need enough. Round down when you must not go over. Keep the exact number when it has to match.
Lean one way	Round both numbers down: the estimate is never more than the sum. Round both up: it is never less than the sum. For a difference, round the first down and the second up. The estimate is never more than the difference.
Quick times	Times 5 is times 10, then half. Times 25 is times 100, then a quarter. Times 125 is times 1000, then an eighth.

One page holds 10,000 dots. How many pages hold one lakh dots?

10
100
1,000

A note says 1,00,000 bricks. A bill says 100,000 bricks. What is the difference in the loads?

The bill is bigger, because its commas sit in different places
There is none — the same six digits, in two comma patterns
The note is bigger, because it carries an extra comma

How is 3,00,45,000 read out loud?

Three crore forty-five thousand
Three lakh forty-five thousand
Three crore forty-five lakh

Which is bigger, 99,99,999 or 1,00,00,000?

99,99,999, because it starts with a 9
1,00,00,000
They are equal, because both are just under a crore

What is 4,999 rounded to the nearest thousand?

4,000, because you cross out the last three digits
4,900, because you change the last two digits to 0
5,000

A cart carries 1,480 bricks and 260 carts arrive. Someone claims the total is 38,48,000. Does that pass the size check?

Yes — it is close enough to be worth keeping
There is no way to tell without doing the exact multiplication
No. Round to 1,500 × 300 = 4,50,000. 38,48,000 is far above double that

Count one thing every second. A lakh takes a little over a day. Roughly how long does a crore take?

About ten days, because a crore is ten lakh
About 116 days, because a crore is a hundred lakh
About a year, because big numbers take a long time

A class of 52 students needs one chair each. Chairs come in stacks of 10. How many chairs should you order?

60
50, the nearest ten
52, the exact count

You round 4,38,000 and 2,61,000 both up to a lakh. You add and get 8,00,000. What do you know about the real sum?

It is less than 8,00,000
It is more than 8,00,000
It is exactly 8,00,000

Which line gives 52 × 25 by the quick way?

Half of 52 is 26, then 26 × 100 = 2,600
52 × 10 = 520, then half is 260
52 × 100 = 5,200, then a quarter is 1,300

Part I, Chapter 1 of your textbook is Large Numbers Around Us. You have named the columns and moved the commas. You have drawn a lakh out in dots. Now read the chapter and try its questions.

Next: Arithmetic Expressions. Reading a calculation as a recipe. Finding out why the order you work in changes the answer.

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