## Chapter 1 Knowing our Numbers Exercise 1.3

**Question 1: Estimate each of the following using general rule:**

a) 730 + 998

b) 796 - 314

c) 12,904 + 2,888

d) 28,292 - 21,496

Make ten more such examples of addition, subtraction and estimation of their outcome.

Answer:

a) 730 + 998

b) 796 - 314

c) 12,904 + 2,888

d) 28,292 - 21,496

Make ten more such examples of addition, subtraction and estimation of their outcome.

Answer:

a)

Round off to hundreds

730 rounds off to 700

998 rounds off to 1000

= 700 + 1000 = 1700

b)

Round off to hundreds

796 rounds off to 800

314 rounds off to 300

= 800 - 300 = 500

c)

Round off to thousands

12904 rounds off to 13000

2888 rounds off to 3000

= 13000 + 3000 = 16000

d)

Round off to thousands

28292 round off to 28000

21496 round off to 21000

= 28000 - 21000 = 7000

Ten examples of such addition and subtraction are

i) 460 + 290

Round off to hundreds

460 round off to 500

290 round off to 300

= 500 + 300 = 800

ii) 3999 + 5100

Round off to thousands

3999 round off to 4000

5100 round off to 5000

= 4000 + 5000 = 9000

iii) 611 - 455

Round off to hundreds

611 round off to 600

455 round off to 500

= 600 - 500 = 100

iv) 5440 - 2972

Round off to thousands

5440 round off to 5000

2972 round off to 3000

= 5000 - 3000 = 2000

v) 2091 + 9845

Round off to thousands

2091 round off to 2000

9845 round off to 10000

= 2000 + 10000 = 12000

vi) 1990 - 1292

Round off to thousands

1990 round off to 2000

1292 round off to 1300

= 2000 - 1300 = 700

vii) 9100 + 5750

Round off to thousands

9100 round off to 9000

5750 round off to 6000

= 9000 + 6000 = 15000

viii) 6400 + 4900

Round off to thousands

6400 round off to 6000

4900 round off to 5000

= 6000 + 5000 = 11000

ix) 3731 - 1300

Round off to thousands

3731 round off to 4000

1300 round off to 1000

= 4000 - 1000 = 3000

x) 6885 - 4356

Round off to thousands

6885 round off to 7000

4356 round off to 4000

= 7000 - 4000 = 3000

**Question 2: Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens):**

a) 439 + 334 + 4,317

b) 1,08,734 - 47,599

c) 8325 - 491

d) 4,89,348 - 48,365

Make four more such examples.

Answer:

a) 439 + 334 + 4,317

b) 1,08,734 - 47,599

c) 8325 - 491

d) 4,89,348 - 48,365

Make four more such examples.

Answer:

a)

Rounding off to nearest hundreds

439 round off to 400

334 round off to 300

4317 round off to 4300

= 400 + 300 + 4300 = 5000

Rounding off to nearest tens

439 round off to 440

334 round off to 330

4317 round off to 4320

= 440 + 330 + 4320 = 5090

b)

Rounding off to nearest hundreds

1,08,734 round off to 108700

47,599 round off to 47600

= 108700 - 47600 = 61100

Rounding off to nearest tens

1,08,734 round off to 108730

47,599 round off to 47600

= 108730 - 47600 = 61130

c)

Rounding off to nearest hundreds

8325 round off to 8300

491 round off to 500

= 8300 - 500 = 7800

Rounding off to nearest tens

8325 round off to 8330

491 round off to 490

= 8330 - 490 = 7840

d)

Rounding off to nearest hundreds

489348 round off to 489300

48365 round off to 48400

= 489300 - 48400 = 440900

Rounding off to nearest tens

489348 round off to 489350

48365 round off to 48370

= 489350 - 48370 = 440980

Four examples of such are

i) 4899 + 662

Rounding off to nearest hundreds

4899 round off to 4900

662 round off to 700

= 4900 + 700 = 5600

Rounding off to nearest tens

4899 round off to 4900

662 round off to 660

= 4900 + 660 = 5560

ii) 770 - 310

Rounding off to nearest hundreds

770 round off to 800

310 round off to 300

= 800 - 300 = 400

Rounding off to nearest tens

770 round off to 770

310 round off to 310

= 770 - 310 = 460

iii) 63740 - 28759

Rounding off to nearest hundreds

63740 round off to 63700

28759 round off to 28600

= 63700 – 28600 = 35100

Rounding off to nearest tens

63740 round off to 63740

28759 round off to 28760

= 63740 - 28760 = 34980

iv) 8972 + 3548

Rounding off to nearest hundreds

8972 round off to 9000

3548 round off to 3500

= 9000 + 3500 = 12500

Rounding off to nearest tens

8972 round off to 8970

3548 round off to 3550

= 8970 + 3550 = 12520

**Question 3: Estimate the following products using general rule:**

a) 578 × 161

b) 5281 × 3491

c) 1291 × 592

d) 9250 × 29

Make four more such examples.

Answer:

a) 578 × 161

b) 5281 × 3491

c) 1291 × 592

d) 9250 × 29

Make four more such examples.

Answer:

a)

Rounding off by general rule

578 round off to 600

161 round off to 200

600 × 200 = 120000

b)

Rounding off by general rule

5281 round off to 5000

3491 round off to 3500

= 5000 × 3500 = 17500000

c)

Rounding off by general rule

1291 round off to 1300

592 round off to 600

= 1300 × 600 = 780000

d)

Rounding off by general rule

9250 round off to 9000

29 round off 30

= 9000 × 30 = 270000

Four examples of such are

i) 5340 × 89

Rounding off by general rule

5340 round off to 5000

89 round off 90

= 5000 × 90 = 450000

ii) 998 × 115

Rounding off by general rule

998 round off to 1000

115 round off to 120

= 1000 × 120 = 120000

iii) 4888 × 654

Rounding off by general rule

4888 round off to 4900

654 round off to 700

= 4900 × 700 = 3430000

iv) 382 x 1062

Rounding off by general rule

382 round off to 400

1062 round off to 1000

= 400 x 1000 = 400000

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