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Knowing Our Numbers

Knowing Our Numbers


Exercise 1.3


Ex 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

solution-

(a) 730 + 998

Round off 730 to = 700
Round off 998 to = 1,000
∴ 730 + 998 = 700 + 1000 = 1700

(b) 796 – 314

Round off 796 to = 800
Round off 314 to = 300
∴ 800 – 300 = 500

(c) 12,904 + 2,888

Round off 12,904 to = 13000
Round off 2888 to = 3000
∴ 13000 + 3000 = 16000

(d) 28,292 – 21,496

Round off 28,292 to = 28,000
Round off 21,496 to = 21,000
∴ 28,000 – 21,000 = 7,000


Ex 1.3  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) 8,325-491
(d) 4,89,348-48,365

solution-

(a)439 + 334 + 4,317

(Rounding off to nearest hundreds)-

Round off 439 to = 400
Round off 334 to = 300

Round off 4317 to = 4300

∴ 400 + 300 + 4300 = 5,000

(Rounding off to nearest tens)-

Round off 439 to = 440
Round off 334 to = 330

Round off 4317 to = 4320

∴ 440 + 330 + 4320 = 5090

(b) 1,08,734 – 47,599

(Rounding off to nearest hundreds)-

Round off 1,08,734 to = 1,08,700
Round off 47,599 to =47,600

∴ 1,08,700 – 47,600 = 61,100

(Rounding off to nearest tens)-

Round off 1,08,734 to = 1,08,730
Round off 47,599 to =47,600

∴ 1,08,730 – 47,600 = 61,130.

(c) 8325 – 491

(Rounding off to nearest hundreds)-

Round off 8325 to = 8300
Round off 491 to = 500
∴ 8300 – 500 = 7800

(Rounding off to nearest tens)-

Round off 8325 to = 8330
Round off 491 to = 490
∴ 8330 – 490 = 7840.

(d) 4,89,348 – 48,365

(Rounding off to nearest hundreds)-

Round off 4,89,348 to = 4,89,300
Round off 48,365 to = 48,400
∴ 4,89,300 – 48,400 = 4,40,900

(Rounding off to nearest tens)-

Round off 4,89,348 to = 4,89,350
Round off 48,365 to = 48,370
∴ 4,89,350 – 48,370 = 4,40,980


Ex 1.3  Question 3.


Estimate the following products using the general rule:
(a) 578 x 161
(b)5281 x 3491
(c) 1291 x 592
(d) 9250 x 29
Solution-

(a) 578 x 161

Round off 578 to = 600
Round off 161 to = 200
∴ 600 x 200 = 1,20,000

(b) 5281 x 3491

Round off 5281 to = 5000
Round off 3491 to = 3000
∴ 5000 x 3000 = 1,50,00,000

(c) 1291 x 592

Round off 1291 to = 1300
Round off 592 to = 600
∴ 1300 x 600 =7,80,000

(d) 9250 x 29

Round off 9250 to = 9000
Round off 29 to = 30
∴ 9000 x 30 = 2,70,000


 

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