Page 9 - SM inner class 6.cdr

ten thousand. The number 78,988 rounded to Example 3. Estimate the sum 5290 + 17986 by
the nearest ten thousand would be 80,000. rounding off the numbers to their nearest
hundreds and compare with actual sum .
Rounding to the Nearest Lakh Solution: (i) Estimating the numbers 5290

Large numbers are often rounded off to and 17986 to their nearest hundreds, we get
5300 and 18000 respectively.
nearest lakh
We have,
To round numbers to the nearest lakh, make
5300
the numbers whose last five digits are 00001
+18000
through 49999 into the previous lower number
23300
that ends in 00000.
Actual Sum = 5290 + 17986 = 23276
For example:– 7,17,584 rounded to the nearest
lakh would be 7,00,000. Here estimated sum > actual sum
Numbers that have the last five digits of 50000 As 23300>23276
or more should be rounded up to the next even Example 4. Give a rough estimate and also a
lakh. The number 6,71,648 rounded to the closer estimate of 489342 - 48365.
nearest lakh would be 7,00,000. Solution: We have, 489342 - 48365 = 440977

Estimation To find rough estimate, let us round off each
number to nearest ten thousands.
To estimate means to find something close to
the correct answer. In other words, you are 489342 rounds off as 490000
approximating. 48365 rounds off as 50000
For example, the American statistic for the Estimated difference = 490000 - 50000 = 440000
ideal number of children is 2.5. Now,
So, rough estimate = 440000
obviously, nobody can have half a kid. We can
estimate this exact statistic to either 2 or 3 In order to obtain a closer estimate, let us
children. round off each number to nearest thousands.
Now take another example:– A trader is to 489342 rounds off as 489000
receive money from two sources. The money he 48365 rounds off as 48000
is to receive is ` 13,569 from one source and
Estimated difference = 489000 - 48000
` 26,785 from an other. He has to pay ` 37,000
= 441000
to some one else by the eve ning. He rounds off
the numbers to their near est thousands as Clearly, it is closer to the actual difference
` 13,569 as ` 14,000 and ` 26,785 as ` 27,000 440977
and quickly works out the rough an swer which Hence, closer estimate is 441000.
is near to ac cu rate answer, that he would have
Example 5. Use the method to estimate the
(14000 27000 = ` 41 ,000 by the eve ning.
+
)
product:– 562 ´ 233.
So estimation make our calculation fast and
Solution: 562 ® 600
easy. It works great in our daily life and save
233 ® 200
our precious time and energy. But one thing is
´
,
,
sure that it gives approximate answer. 600 200 =1 20 000
Example 6. Use the method to estimate the
Estimation by rounding off the numbers
quotient– 5875 ÷ 517.
It is very popular and commonly used method. Solution: 5875 ® 6000
The numbers are rounded off to nearest tens,
517 ® 500
hundreds, thousands and so on.
¸
6000 500 =12
Let’s take some examples–
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Mathematics In Focus - 6