**Textbook: Exercise 3.3 (p69)**

(a) 5837 + 985 = (est) 7000

(b) 347 - 482 + 650 = (est) -500

(c) 23.92 x 4.801 = (est) 1200

(e) 62.47 x 0.093 ÷ 0.00217 = (est) 40000

In the comments,

- Write down if each estimated value is reasonable?
- Justify your answer with working.

(a) 5837+ 985≈ (est)7000

ReplyDelete(b)347-482+650≈ (est)500

(c)23.92x4.801≈ (est)120

(e)60x0.1÷0.002≈(est)3000

(b),(c) and (e) are wrong

This comment has been removed by the author.

ReplyDeleteThe estimated answers of b, c and e are unreasonable.

ReplyDeleteb should be 347-482+650≈300-500+700(1SF)

=500

c should be 23.92 X 4.801≈24X5 (1SF)

=120

e should be 62.47X0.093÷0.00217≈62X0.09÷0.002(1SF)

=2.835

This comment has been removed by the author.

ReplyDelete(a) 5837 + 985 ≈ 6000 + 1000

ReplyDelete= 7000

Yes, (a) is reasonable.

(b) 347 - 482 + 650 ≈ 300 - 500 + 700

= -200 + 700

= -500

Yes, (b) is reasonable.

(c) 23.92 x 4.801 ≈ 24 x 5

= 120

No, (c) is not reasonable.

(e) 62.47 x 0.093 ÷ 0.00217 ≈ 62 x 0.09 ÷ 0.002

= 5.58 ÷ 0.002

= 2.790

No, (e) is not reasonable.

(a) 5837 + 985 = 6822 (reasonable)

ReplyDelete(b) 347 - 483 + 650

≈ 135 + 650

515(not reasonable )

(c) 23.92 x 4.801 = 114.83992(not reasonable)

(d) 62.47 x 0.093 ÷ 0.00217 = 2 677 28571 (not reasonable)

(a)5837 + 985 = 6822 (reasonable)

ReplyDelete(b)347 - 482 + 650

=-135 + 650

=515 (not reasonable)

(c)23.92 x 4.801

=114.83992 (not reasonable)

(d)62.47 x 0.093 ÷ 0.00217 = 2 677.28571 (not reasonable)

a)5837 + 985=(est) 6000 + 1000

ReplyDelete= 7000

Therefore, the estimated value of (a) is reasonable.

b)347 - 482 + 650≈(est) 300 - 500 + 700

=(-200) + 700

=500

The estimated value of (b) is not reasonable; the answer should be (+)500 instead of -500.

c) 23.92 x 4.801≈(est) 20 x 5

=100

The estimated value of (c) is not reasonable; the answer is 100 instead of 1200.

e) 62.47 x 0.093 ÷ 0.00217≈(est) 60 x 0.09 ÷ 0.002

= 5.4 ÷ 0.002

=2700

The estimated value of (e) is not reasonable; the answer is 2700 instead of 40 000.

ALL answers are rounded off to the 1st significant number.

a)5837 + 985 ≈ 6000 + 1000

ReplyDelete= 7000

b)Not reasonable because

347 - 482 + 650 ≈ 300 - 500 + 700

= 500

c) Not reasonable because

23.92 x 4.801 ≈24 x 4

=96

d)62.47 x 0.093 ÷ 0.00217 ≈ 62 x 0.1

= 6.2

No, (b), (c), and (e) is not reasonable. (a) is reasonable.

ReplyDelete(a) 5837+985≈6000+1000

=7000

(b) 347-482+650

I think that (a) is reasonable as the sum is rounded off to the nearest thousands.

ReplyDeleteI think that (b) is unreasonable as the estimated answer is suppose to be 500(300-500+700) and not -500.

I think that (c) is unreasonable as the estimated answer is suppose to be 120(24x5) and not 1200.

a= Reasonable

ReplyDelete6000+1000=7000

b=Unreasonable

400-500+700=500

c=Unreasonable

20x5=100

e=Unreasonable

60x0.09÷0.002=2700

a) 5837 + 985≈6000+1000

ReplyDelete=7000

(b) 347 - 482 + 650≈300-500+700

=500

(c) 23.92 x 4.801≈20 x 5

=100

(e) 62.47 x 0.093 ÷ 0.00217 ≈ 60 x 0.09 ÷ 0.002

= 5.4 ÷ 0.002

(a) It is reasonable as the numbers are rounded off to 1 significant figure.

ReplyDelete(b) It is unreasonable.

347 - 482 + 650 ≈ 300 - 500 + 700

= -200+700

= 500

The answer is not -500 but 500.

(c) 23.92 x 4.801 ≈ 20 x 5

= 100

(e) 62.47 x 0.093 0.00217 ≈ 60 x 0.09 ÷ 0.002

= 2790

(a) Exact value: 5837 + 985 = 6822 (reasonable)

ReplyDelete(b) Exact value: 347-482+650 = 515 (not reasonable)

(c) Exact value : 23.92 x 4.801 = 114.83992 (not reasonable)

(d) 62.47 x 0.093 ÷0.00217 = 2677.28571 (not reasonable)

chengngee

a) reasonable

ReplyDeleteWorking:

a) 5837+ 985 ≈ 6000+ 1000

= 7000

b) unreasonable

Working

b) 347-482+650 ≈ 300-500+700

= 500

Part 1

It is reasonable.

ReplyDelete5837+985≈6000+1000

=7000

It is not reasonable.

347 - 482 + 650 ≈300-500+700

= 500

It is not reasonable.

23.92 x 4.801≈20×5

=100

62.47 x 0.093 ÷ 0.00217≈60×0.09÷0.002

= 2700

a) reasonable

ReplyDelete5837+985≈6000+1000

=7000

b) reasonable

347-482+650≈ 300-500+700

= (-200) + 700

=-900

c) unreasonable

23.92 x 4.801≈ 24x5

=120

e) unreasonable

62.47x0.093÷0.00217≈ 62x0.1÷0.002

= 6.2÷0.002

= 3100

(a) 5837+985≈ 6000+1000

ReplyDelete= (est)7000

(b) 347-482+650≈ 300-500+700

= (est) 500

(c) 23.92x4.801≈ 24x5

= (est) 120

(e) 62.47x0.093÷0.00217≈ 62x0.1÷0.002

= (est) 3100

(b), (c) and (e) are not reasonable.

Part 2

ReplyDeletec) unreasonable

Workings:23.92x 4.801≈24x 5

=120

e) unreasonable

Workings: 62.47x0.093≈ 60x0.1÷0.002

=3000

(a) 5837 + 985 = (est) 7000

ReplyDelete5837 + 985 ≈ 6000 + 1000

= 7000

(b) 347 - 482 + 650 = (est) -500

347 - 482 + 650 ≈300-500+700

= 500

(c) 23.92 x 4.801 = (est) 1200

23.92 x 4.801 ≈24 x 5

= 120

(e) 62.47 x 0.093 ÷ 0.00217 = (est) 40000

62.47 x 0.093 ÷ 0.00217 ≈ 60 x 0.09 ÷ 0.002

=2700

Follow-up:

ReplyDelete(a) 5837 + 985 = 6822

(b) 347 - 482 + 650 = 515

(c) 23.92 x 4.801 ≈ 114

(e) 62.47 x 0.093 ÷ 0.00217 ≈ 2677

As comparing to the estimation, (a) is reasonable & (b),(c),(d) is not reasonable.

(a) is reasonable as both numbers are rounded off to 1 significant figure.

ReplyDelete(b) It is not reasonable.

347-482+650≈-135+650

=515

(c) 23.92 x 4.801 ≈ 114(unreasonable)

(e) 62.47 x 00.093 ÷ 0.00217≈ 2677(unreasonable)