NCERT Class 6 Solutions: Knowing Your Numbers (Chapter 1) Exercise 1.3 – Part 1
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Q1 Estimate each of the following using general rule:
Solution:


By rounding off to hundreds

730 rounds off to 700 and 998 rounds off to 1000.

Estimate sum is 1700



By rounding off to hundreds

796 round off to 800 and 314 round off to 300

Estimate difference is 500



By rounding off two nearest thousands

12904 round off to 13000 and 2888 round off to 3000.

Estimate sum is 16000



By rounding off to nearest thousands

28292 rounds off to 28000 and 21496 rounds off to 21000.

Estimate diffrence is 7000
Q2 Give a rough estimate (by rounding numbers off to nearest hundreds before calculation) and also a closer estimate (by rounding off to nearest tens):
How to Round Numbers
Decide which is the last digit to keep, for example when off to rounding to hundreds the units and tens digit will become zero and the hundreds digit will be kept. So we will be working on the hundreds digits
Leave it the same if the next digit is less than 5 (this is called rounding down)
Increase it by 1 if the next digit is 5 or more (this is called rounding up)
Example 1: To round 764 to the nearest 100

We look at the digit right after the hundred’s digit

Since it is 6 the 7 in the hundreds place is changed to 8 and the answer becomes 800.
Example 2: Round 86 to the nearest 10

We want to keep the "8"

The next digit is "6" which is 5 or more, so increase the "8" by 1 to "9"
Answer: 90. We say that 86 gets "rounded up"
Rounding can be understood with a roller coaster:
Here are 2 examples:
Solution:


By rounding off to nearest hundreds

439 rounds off to 400, 334 rounds off to 300 and 4317 rounds off to 4300

The digit we need to look at to decide the value of hundreds digit is underlined

By rounding off to nearest tens

439 rounds off 440, 334 rounds off 330 and 4317 rounds off 4320

The digit we need to look at to decide the value of tens digit is underlined



By rounding off to nearest hundreds

108737 rounds off 108700, 47599 rounds off 47600

The digit we need to look at to decide the value of hundreds digit is underlined

By rounding off to nearest tens

108737 rounds off 108730, 47599 rounds off 47600

The digit we need to look at to decide the value of tens digit is underlined



By rounding off to nearest hundreds

8325 rounds off 8300, 491 rounds off 500

The digit we need to look at to decide the value of hundreds digit is underlined

By rounding off to nearest tens

8325 rounds off 8330, 491 rounds off 490

The digit we need to look at to decide the value of tens digit is underlined



By rounding off to nearest hundreds

489348 rounds off 489300, 48365 rounds off 48400

By rounding off to nearest tens

489348 rounds off 489350, 48365 rounds off 48370