CONCEPT OF APPROXIMATION
Rounding Numbers
A rounded number has about the same value as the number you start with, but it is less exact.
For example, 341 rounded to the nearest hundred is 340. That is because 341 is closer in value to 340 than to 350. When rounding off to the nearest rupee, Rs.1.89 becomes Rs.2.00, because Rs.1.89 is closer to Rs.2.00 than to Rs.1.00
Rules for Rounding
- If the number you are rounding is followed by 5, 6, 7, 8, or 9, round the number up. Example: 38 rounded to the nearest ten is 40
- If the number you are rounding is followed by 0, 1, 2, 3, or 4, round the number down. Example: 33 rounded to the nearest ten is 30
When rounding a number, you first need to ask: what are you rounding it to? Numbers can be rounded to the nearest ten, the nearest hundred, the nearest thousand, and so on.
Consider the number 4,827.
- 4,827 rounded to the nearest ten is 4,830
- 4,827 rounded to the nearest hundred is 4,800
- 4,827 rounded to the nearest thousand is 5,000
Rounding Decimals and Fractions
Rounding fractions works exactly the same way as rounding whole numbers. The only difference is that instead of rounding to tens, hundreds, thousands, and so on, you round to tenths, hundredths, thousandths, and so on.
- 7.8199 rounded to the nearest tenth is 7.8
- 1.0621 rounded to the nearest hundredth is 1.06
- 3.8792 rounded to the nearest thousandth is 3.879
Here's a tip: to avoid getting confused in rounding long decimals, look only at the number in the place you are rounding to and the number that follows it. For example, to round 5.3824791401 to the nearest hundredth, just look at the number in the hundredths place—8—and the number that follows it—2. Then you can easily round it to 5.38.
Now try to solve these 10 questions as fast as possible (5-7 min)
1. (1702 / 68) x 136.05=?
(a) 3500 (b) 3550
(c) 3450 (d) 3400
2. (16.5/100) x 2400 =2/3 of ?
(a) 588 (b) 594
(c) 592 (d) 590
3. (2959.85 / 16.001) – 34.99 =?
(a) 160 (b) 150
(c) 140 (d) 180
4. 99999 / 999/ 99 / 9 =? / 100 ( where ‘/’ denotes division)
(a) 1 (b) 10
(c) 100 (d) 1000
5. 30.002 x (603.2 / 19.9)=2 x (?)
(a) 550 (b) 600
(c) 450 (d) 900
6. (3.5 x 1.4)/0.7=?
(a) 7.1 (b) 3.5
(c) 0.7 (d) 2.4
7. 14.28% of 49 =?
(a) 8 (b) 11
(c) 7 (d) 16
8. 69.69 - 50.54 + 74.65 =? + 30.42
(a) 60 (b) 65
(c) 70 (d) 55
9. (50.48 x 19.87) – 14.99 + 99.978 =?
(a) 1005 (b) 1115
(c) 1085 (d) 1045
10. 30.4587 + 14.768 x 25.843 – 15.620 =? - 9.95
(a) 350 (b) 380
(c) 390 (d) 400
SOLUTIONS
1 d 2 b 3 b 4 b 5 c
6 a 7 c 8 b 9 c 10 d
Time taken
Within 5 min: EXCELLENT
5-7 min: YOU CAN DO BETTER
More than 7 min: YOU NEED TO WORK HARD
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