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.
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.
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.
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Answers
Answer:
Step-by-step explanation:
(a) 730+998730+998
Rounding of to nearest hundred
730\Rightarrow700730⇒700 and 998\Rightarrow1,000998⇒1,000
730+998\ \Rightarrow\ 700+1,000730+998 ⇒ 700+1,000
= 1,700
(b) 796-314796−314
Rounding of to nearest hundered
796\Rightarrow800\ \ and\ \ 314\Rightarrow300796⇒800 and 314⇒300
796-314\ \Rightarrow\ 800-300796−314 ⇒ 800−300
= 500
(c) 12,904+2,88812,904+2,888
Rounding off to nearest thousand
12,904\Rightarrow13,000\ \ and\ \ 2,888\Rightarrow3,000\12,904⇒13,000 and 2,888⇒3,000 12,904+2,888\ \Rightarrow\ 13,000+3,00012,904+2,888 ⇒ 13,000+3,000
= 16,000
(d) 28,292-21,49628,292−21,496
Rounding off to nearest thousand
28,292\Rightarrow28,000\ \ and\ \ 21,496\Rightarrow21,00028,292⇒28,000 and 21,496⇒21,000
28,292-21,496\ \Rightarrow\ 28,000-21,00028,292−21,496 ⇒ 28,000−21,000
= 7,000
10 more examples :-
Example 1:
1,246+5,822\ \Rightarrow\ 1,200+6,000\ =\ 7,2001,246+5,822 ⇒ 1,200+6,000 = 7,200
Example 2:
333+737\ \Rightarrow\ 300+700\ =\ 1,000333+737 ⇒ 300+700 = 1,000
Example 3:
23,489-13,503\ \Rightarrow\ 23,000-14,000\ =\ 9,00023,489−13,503 ⇒ 23,000−14,000 = 9,000
Example 4:
11,307-10,312\Rightarrow\ 11,000-10,000\ =\ 1,00011,307−10,312⇒ 11,000−10,000 = 1,000
Example 5:
213-189\ \Rightarrow\ 200-200\ =\ 0213−189 ⇒ 200−200 = 0
Example 6:
9,853+9,999\ \Rightarrow\ 10,000+10,000\ =\ 20,0009,853+9,999 ⇒ 10,000+10,000 = 20,000
Example 7:
5,703+5,431\Rightarrow\ 6,000+5,000\ =\ 11,0005,703+5,431⇒ 6,000+5,000 = 11,000
Example 8:
6,423-3,610\ \Rightarrow\ 6,000-4,000\ =\ 2,0006,423−3,610 ⇒ 6,000−4,000 = 2,000
Example 9:
2,876+9,559\ \Rightarrow\ 3,000+10,000\ =\ 13,0002,876+9,559 ⇒ 3,000+10,000 = 13,000
Example 10:
4,639-2,990\ \Rightarrow\ 5,000-3,000\ =\ 2,0004,639−2,990 ⇒ 5,000−3,000 = 2,000
(a) 439+334+4,317439+334+4,317
Rough estimate-
439+334+4,317\ \Rightarrow400+300+4,300\ =5,000439+334+4,317 ⇒400+300+4,300 =5,000
Closer estimate-
439+334+4,317\ \Rightarrow440+330+4,320\ \Rightarrow\ 5,090439+334+4,317 ⇒440+330+4,320 ⇒ 5,090
(b) 1,08,734-47,5991,08,734−47,599
Rough estimate-
1,08,734-47,599\ \Rightarrow1,08,700-47,600\ \Rightarrow61,1001,08,734−47,599 ⇒1,08,700−47,600 ⇒61,100
Closer estimate-
1,08,734-47,599\ \Rightarrow1,08,730-47,600\ =61,1301,08,734−47,599 ⇒1,08,730−47,600 =61,130
(c) 8,325-4918,325−491
Rough estimate-
8,325-491\ \Rightarrow8,300-500\ =7,8008,325−491 ⇒8,300−500 =7,800
Closer estimate-
8,325-491\ \Rightarrow8,330-490\ =7,8408,325−491 ⇒8,330−490 =7,840
(d) 4,89,348-48,3654,89,348−48,365
Rough estimate-
4,89,348-48,365\ \Rightarrow4,89,300-48,400\ =4,40,9004,89,348−48,365 ⇒4,89,300−48,400 =4,40,900
Closer estimate-
4,89,348-48,365\ \Rightarrow4,89,350-48,370\ =4,40,9804,89,348−48,365 ⇒4,89,350−48,370 =4,40,980
Four more such examples:
Example 1: 484+662484+662
Rough estimate-
484+662\ \Rightarrow500+700\ =1,200484+662 ⇒500+700 =1,200
Closer estimate-
484+662\ \Rightarrow480+660\ =1,140484+662 ⇒480+660 =1,140
Example 2: 8,768-3,8178,768−3,817
Rough estimate-
8,768-3,817\ \Rightarrow8,800-3,800\ =5,0008,768−3,817 ⇒8,800−3,800 =5,000
Closer estimate-
8,768-3,817\ \Rightarrow8,770-3,820\ =4,9508,768−3,817 ⇒8,770−3,820 =4,950
Example 3: 6,763+9,7656,763+9,765
Rough estimate-
6,763+9,765\ \Rightarrow6,800+9,800\ =16,6006,763+9,765 ⇒6,800+9,800 =16,600
Closer estimate-
6,763+9,765\ \Rightarrow6,760+9,770\ =16,5306,763+9,765 ⇒6,760+9,770 =16,530
Example 4: 3,828-1,2823,828−1,282
Rough estimate-
3,828-1,282\ \Rightarrow3,800-1,300\ =2,5003,828−1,282 ⇒3,800−1,300 =2,500
Closer estimate-
3,828-1,282\ \Rightarrow3,830-1,280\ =2,5503,828−1,282 ⇒3,830−1,280 =2,550
(a)578\times161578×161
Rounding off using general rule
578\Rightarrow600\ \ and\ \ 161\Rightarrow200578⇒600 and 161⇒200
So, 600\times200\ =\ 1,20,000600×200 = 1,20,000
(b) 5,281\times3,4915,281×3,491
Rounding off using general rule
5,281\Rightarrow5,000\ \ and\ \ 3,491\Rightarrow3,0005,281⇒5,000 and 3,491⇒3,000
So, 5,000\times3,000\ =\ 1,50,00,0005,000×3,000 = 1,50,00,000
(c) 1,291\times5921,291×592
Rounding off using general rule
1,291\Rightarrow1,300\ \ and\ \ 592\Rightarrow6001,291⇒1,300 and 592⇒600
So, 1,300\times600\ =\ 7,80,0001,300×600 = 7,80,000
(d) 9,250\times299,250×29
Rounding off using general rule
9,250\Rightarrow9,000\ \ and\ \ 29\Rightarrow309,250⇒9,000 and 29⇒30
So, 9,000\times30\ =\ 2,70,0009,000×30 = 2,70,000
Four more such examples:
Example 1: 391\times561\ \Rightarrow400\times600\ =2,40,000391×561 ⇒400×600 =2,40,000
Example 2: 1,125\times2,307\ \Rightarrow1,100\times2,300\ =\ 25,30,0001,125×2,307 ⇒1,100×2,300 = 25,30,000
Example 3:
54\times3,019\ \Rightarrow50\times3,000\ =\ 1,50,00054×3,019 ⇒50×3,000 = 1,50,000
Example 4:
3,858\times7,682\ \Rightarrow4,000\times8,000\ =\ 3,20,00,0003,858×7,682 ⇒4,000×8,000 = 3,20,00,000
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