NCERT Class 6 Solutions: Knowing Your Numbers (Chapter 1) Exercise 1.3 – Part 1

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Q-1 Estimate each of the following using general rule:

  1. 730+998

  2. 796314

  3. 12,904+2,888

  4. 28,29221,496

Solution:

  1. 730+998

    • By rounding off to hundreds

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

      Given the two numbers, 730+998 find their estimated sum

      Find the Estimated Value of 730+998

      Given the two numbers, 730+998 find their estimated sum

      Estimatesumis1700

  2. 796314

    • By rounding off to hundreds

    • 796 round off to 800 and 314 round off to 300

      Given the two numbers 796-314, find the estimated diffrence

      Find the Estimated Value of 796-314

      Given the two numbers 796-314, find the estimated diffrence

      Estimatediffrenceis500

  3. 12,904+2,888

    • By rounding off two nearest thousands

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

      Given the two numbers 2904+2888, find the estimated sum

      Given the Two Numbers Are 12904+2888

      Given the two numbers 2904+2888, find the estimated sum

      Estimatesumis16000

  4. 28,29221,496

  • By rounding off to nearest thousands

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

    Given the two numbers 28292-21496, find the estimated diffrence

    Find the Estimated Value of 28292-21496

    Given the two numbers 28292-21496, find the estimated diffrence

    Estimatediffrenceis7000

Q-2 Give a rough estimate (by rounding numbers off to nearest hundreds before calculation) and also a closer estimate (by rounding off to nearest tens):

  1. 439+334+4317

  2. 1,08,73747,599

  3. 8325491

  4. 4,89,34848,365

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:

Numbers 4 or less than 4 are rounded down while numbers 5 or more are rounded up to next digit

4 or Less "Rounded Down" 5 or More Rounded to Next Digit

Numbers 4 or less than 4 are rounded down while numbers 5 or more are rounded up to next digit

Here are 2 examples:

Understanding rounding examples with roller coaster.

Examples of Rounding With Roller Coaster

Understanding rounding examples with roller coaster.

Solution:

  1. 439+334+4317

    • 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

      Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest hundredths

      Find the Estimated Value of 439+334+4317 (Nearest Hundredths)

      Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest hundredths

    • 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

      Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest tens

      Find the Estimated Value of 439+334+4317 (Nearest Tens)

      Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest tens

  2. 1,08,73747,599

    • 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

      Given the three numbers 108737-47599, find the estimated diffrence by first rounding numbers to nearest hundredths

      Find the Estimated Value of 108737-47599 (Nearest Hundredths)

      Given the three numbers 108737-47599, find the estimated diffrence by first rounding numbers to nearest hundredths

    • 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

      Given the three numbers 108737-47599, find the estimated sum by first rounding numbers to nearest tens

      Find the Estimated Value of 108737-47599 (Nearest Tens)

      Given the three numbers 108737-47599, find the estimated sum by first rounding numbers to nearest tens

  3. 8325491

    • 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

      Given the two numbers 8325-491, find the estimated difference by first rounding numbers to nearest hundredths

      Find the Estimated Value of 8325-491 (Nearest Hundredths)

      Given the two numbers 8325-491, find the estimated difference by first rounding numbers to nearest hundredths

    • 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

      Given the three numbers 8325-491, find the estimated sum by first rounding numbers to nearest tens

      Find the Estimated Value of 8325-491 (Nearest Tens)

      Given the three numbers 8325-491, find the estimated sum by first rounding numbers to nearest tens

  4. 4,89,34848,365

  • By rounding off to nearest hundreds

  • 489348 rounds off 489300, 48365 rounds off 48400

    Given the two numbers 489348 & 48365, find the estimated difefrence by first rounding numbers to nearest hundredths

    Find the Estimated Value of 489348-48365 (Nearest Hundredths)

    Given the two numbers 489348 & 48365, find the estimated difefrence by first rounding numbers to nearest hundredths

  • By rounding off to nearest tens

  • 489348 rounds off 489350, 48365 rounds off 48370

    Given 8325-491, find the estimated difference by first rounding numbers to nearest tens

    Find the Estimated Value of 8330-490 (Nearest Tens)

    Given 8325-491, find the estimated difference by first rounding numbers to nearest tens

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