Mathematics – Class 6 – Chapter 1 – Knowing Our Number – NCERT Exercise 1.3 Solutions

Q1. Estimate each of the following using general rule:

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

(a) 730 + 998

Solutions:

 730 + 998

Round off to hundreds

730 is rounds off to 700

998 is rounds off to 1000

Hence, 730 + 998 = 700 + 1000 = 1700

(b) 796 – 314

Solution:

 796 – 314

Round off to hundreds

796 is rounds off to 800

314 is rounds off to 300

Hence, 796 – 314 = 800 – 300 = 500

(c) 12904 + 2888

Solution:

 12904 + 2888

Round off to thousands

12904 is rounds off to 13000

2888 is rounds off to 3000

Hence, 12904 + 2888 = 13000 + 3000 = 16000

(d) 28292 – 21496

Solution:

 28292 – 21496

Round off to thousands

28292 is round off to 28000

21496 is round off to 21000

Hence, 28292 – 21496 = 28000 – 21000 = 7000

Ten more such examples are

(i) 333 + 286 = 300 + 300 = 600

(ii) 3938 + 5995 = 4000 + 6000 = 10000

(iii) 6391 – 3773 = 6000 – 4000 = 2000

(iv) 5434 – 2972 = 5000 – 3000 = 2000

(v) 2175 + 1206 = 2000 + 1000 = 3000

(vi) 1110 – 1292 = 1000 – 1000 = 0

(vii) 910 + 575 = 900 + 600 = 1500

(viii) 6400 – 4900 = 6000 – 5000 = 1000

(ix) 3731 + 1300 = 4000 + 1000 = 5000

(x) 6485 – 4319 = 6000 – 4000 = 2000

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

Make four more such examples.

(a) 439 + 334 + 4317

Solutions:

 439 + 334 + 4317

Rounding off to nearest hundreds

439 + 334 + 4317 = 400 + 300 + 4300

= 5000

Rounding off to nearest tens

439 + 334 + 4317 = 440 + 330 + 4320

= 5090

(b) 108734 – 47599

Solution:

108734 – 47599

Rounding off to nearest hundreds

108734 – 47599 = 108700 – 47600

= 61100

Rounding off to nearest tens

108734 – 47599 = 108730 – 47600

= 61130

(c) 8325 – 491

Solution:

 8325 – 491

Rounding off to nearest hundreds

8325 – 491 = 8300 – 500

= 7800

Rounding off to nearest tens

8325 – 491 = 8330 – 490

= 7840

(d) 489348 – 48365

Solution:

 489348 – 48365

Rounding off to nearest hundreds

489348 – 48365 = 489300 – 48400

= 440900

Rounding off to nearest tens

489348 – 48365 = 489350 – 48370

= 440980

Four more examples are as follows

(i) 4854 + 661

Rounding off to nearest hundreds

4854 + 661 = 4800 + 700

= 5500

Rounding off to nearest tens

4854 + 661 = 4850 + 660

= 5510

(ii) 774 – 390

Rounding off to nearest hundreds

774 – 390 = 800 – 400

= 400

Rounding off to nearest tens

774 – 390 = 780 – 400

380

(iii) 6374 – 2876

Rounding off to nearest hundreds

6374 – 2876 = 6400 – 2900

= 3500

Rounding off to nearest tens

6374 – 2876 = 6380 – 2880

3500

(iv) 8245 – 6313

Rounding off to nearest hundreds

8245 – 6313 = 8200 – 6300

1900

Rounding off to nearest tens

8245 – 6313 = 8240 – 6310

= 1930

Q3. Estimate the following products using general rule:

Make four more such examples.

(a) 578 * 161

Solutions:

 578 * 161

Rounding off by general rule

598 and 161 rounded off to 600 and 200 respectively

600*200 = 120000

(b) 5281 * 3491

Solution:

 5281 * 3491

Rounding off by general rule

5281 and 3491 rounded off to 5000 and 3500 respectively

5000*3500 = 17500000

(c) 1291 * 592

Solution:

 1291 * 592

Rounding off by general rule

1291 and 592 rounded off to 1300 and 600 respectively

1300 * 600 = 780000

(d) 9250 * 29

Solution:

 9250 * 29

Rounding off by general rule

9250 and 29 rounded off to 9000 and 30 respectively

9000 * 30 = 270000

Four more examples are as follows

(i)199 * 29

 Rounding off by general rule

199 and 29 rounded off to 200 and 30 respectively

200 * 30 = 6000

(ii) 398 * 30

Rounding off by general rule

400 and 30 is rounded off to 400 and 30 respectively

400 * 30 = 12000

(iii)556 * 46

Rounding off by general rule

556 and 46 is rounded off to 560 and 50 respectively

560 * 50 = 28000

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