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Large Numbers Around Us

Round which way?

Paper cups come in packs of 10. You need one cup for each of 143 children. How many packs do you buy?

Packs hold 10. There are 143 children.
Step 1 of 4
  1. Packs hold 10. There are 143 children.
  2. Down to 140. Three children get no cup.
  3. Up to 150. Seven cups are spare.
  4. Here, spare is better than short.

15 packs give 150 cups. That is enough for 143 children.

The rule

The nearest ten is 140. But 140 cups are not enough for 143 children. So 140 is not the best answer here. What you need decides whether to round up or down.

Round up when you need enough. Round down when you must not go over. Keep the exact number when it has to match.

Three needs, three answers
You needWayExample
EnoughUp143 children, packs of 10: buy 150
Not to go overDownYou have ₹3,740. The shop takes only ₹500 notes: pay ₹3,500
A matchExactRoom number 417 stays 417

Sometimes up and down are both fine. A stadium sells 48,213 tickets. A news report may say about 48,000.

Tap the number that fits each situation in the lab.

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This track

  1. 0 Start here
  2. 1 Past the thousands column
  3. 2 Two ways to group the same digits
  4. 3 Reading a large number out loud
  5. 4 Which large number is bigger
  6. 5 Rounding to a place you choose
  7. 6 Estimate before you compute
  8. 7 How big a lakh really is
  9. 8 Round which way?
  10. 9 Estimates on one side of the answer
  11. 10 Quick times 5, 25 and 125
  12. 11 Checkpoint: rounding and quick times
  13. 12 The big picture
  14. 13 Track quiz

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