N8 Numbers - Rounding Off

ESTIMATION(L4)

Rounding numbers to the nearest tens/hundreds/thousands is a way of estimating numbers to the nearest tens/hundreds/thousands.

                          Symbol   ≈

Example:

Round 4300 to the nearest thousand.

Method (number line)

Step 1: 4300 is between 4000 and 5000. Draw number line from 4000 to 5000. Mark 4500 (mid-point) and 4300

                     

Step2: 4300 is between 4000 and 4500, then 4000 can be an estimate of 4300

            => 4300 round to the nearest thousand is 4000

Step3: Write Answer

            4300 ≈ 4000

ROUNDING OFF(L5)

Rounding a number is to replace it with another number value that is approximately equal but ‘cleaner’ and simpler. 

Why round-off

1. For easier communication:

It is simpler to say

‘My toy costs about $6.’ rather than ‘My toy costs  

$5.99.

2. Simpler report:

     Average price of soft drink is $1.10, instead of $1.1175

If number is from 0 and to 4, then DROP or Fall (4) off / let it go

If number is from 5 to 9, then ADD 1 or high 5 --> go higher

METHOD to do ROUNDING OFF

Step 1: Underline the rounded off place value given in the question.

a.    If round-off to 10, underline the 10 place

b.    If round-off to 100, underline the 100 place, and so forth

Step 2: Circle the number on the right

Step 3: Compare

         a. Circled number is equal or greater than 5 (5, 6,7,8,9)

-> ADD1: round-UP, add 1 to underline number

                                        or

         b. Circled number is less than 5 (4,3,2,1,0)

-> DROP: round-DOWN, leave underline number un-change

Step 4: Change(Transform) the numbers to the right to 0

Example1: 
     Round off to the nearest ten, 5862

Step1:   5863 – Underline round-off tenth place -> 6

Step2: 586③ – Circle number to the right -> 3

Step3: Compare: 3 is less than 5,

             DROP: round down -> no change to underline

Step4: Change number to right of underline to 0⑤

Answer = 5860

Example2: Round off to the nearest hundred, 37865

Step1:  37865 – Underline round-off hundredth place -> 8

Step2: 378⑥5– Circle number to the right -> 6

Step3: Compare: 6 is greater than 5,

             ADD 1: Round-up -> 8 increase to 9

Step4: Change numbers to right of underline to 0

             Answer = 37900

Practice
     Round off to the nearest thousand, 89569

Step1:  89569 – Underline round-off thousandth place -> 9

Step2: 89⑤69– Circle number to the right ->5

Step3: Compare: 5 equal 5.

             ADD 1 Round-up -> 9 by increasing to 10-> 89 to 90

Step4: Change numbers to right of underline to 0

              Answer = 90000

More Practices

(1) Set 2 numbers for rounding off to the nearest ten and hundred

(2) Request students to set 2 numbers for rounding off to the nearest hundred and thousand.

ROUNDING OFF FOR DECIMAL

Rounding off for decimal is similar to whole numbers except that we need to maintain the decimal places as given in the question.

METHOD

Step 1:  Underline the round-off decimal place required.

Step 2:  Circle the number to the right

Step 3:  Compare

a.    number is 5 or greater, round-UP, ADD 1 to underline number

                              or

b.    Less than 5, round DOWN, DROP, leave underline number un-change

Step 4:  Change numbers to right of underline to 0

Step 5:  Adjust number format

  a. to nearest whole number: drop decimal place

  b. to give decimal places as required

Example1: Round off to the nearest whole number, 5.27

                Step 1:   <Underline whole number> 5.27

                Step 2:  <Circle number to right> 5.②7

                Step 3:  <Compare with 5 > 2 is less than 5, DROP: round-down

                Step 4:  <Change> 5.00,

     Step 5:  <Adjust number format> Answer:  5 (no decimal place)

Example2: Round off to the nearest 1 decimal place, 4.36

                 Step 1:  <Underline 1^st decimal > 4.36        

                 Step 2:  <Circle number to right > 4.3⑥

                 Step 3:  <Compare to 5 >  6 is more than 5,

                                    ADD 1: round-up -> 3 to 4

      Step 4:  <Change> number to the right of underline to 0 ->4.40

                 Step 5:  <Adjust number format> Answer: 4.4 (1 decimal place)

Answer = 4.4

Practice:

1: Round off to the nearest 2 decimal place, 3.295

2: Round off to the nearest 2 decimal place, 3.995

     1: 3.30 [Must write 0 in 3.30 to show nearest 2 decimals]

     2: 4.00[Must write 00 in 4.00 to show nearest 2 decimals]

More Practices

(1) Set 2 numbers for rounding off to the nearest whole number and 1 decimal.

(2) Tutor to request students to set 2 numbers for rounding off to the nearest 1 decimal and 2 decimals.

                  ~~~~ END ~~~~ :)