Estimating Adding And Subtracting Problems
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LearningTranscript
00:00hi kids today we will learn estimates for our addition and subtraction sums
00:09using rounding off techniques we learned so let's get started
00:19we have to add 35 and 61 we have to make a quick estimate rather than actually
00:28adding these numbers for that we will round off 61 and 35 to the nearest 10
00:37and then add them orally to get the estimate for rounding off numbers to the
00:45nearest 10 we see the ones digit if it's less than 5 we round the number down to
00:52the previous 10 that is 60 in this case and if the ones place digit is 5 or more
01:00we round the number up to the next 10 that is 70 in this case here the ones
01:08place digit is 1 that is it's less than 5 so round the whole number to the
01:16previous 10 that is 60 ones place digit in the other number is 5 so we will
01:25round it up to the next and the next 10 here would be 40 so 35 will be rounded
01:33up to 40 adding the rounded off figures 60 and 40 we will get 100 so our
01:44estimate for adding 61 and 35 is 100 if you actually add 61 and 35 you get 96
01:57so our estimate is very close to the actual sum so today we will be
02:05practicing making estimates only let's take another example we have to add
02:13345 and 572 we will be making a quick estimate rather than actually adding
02:24these numbers by rounding off these numbers to the nearest 100 for rounding
02:33off the numbers to the nearest 100 we see the tens digit if it's less than 5
02:40we round it down and if it's greater than equal to 5 we round it up to the
02:48next 100 here 4 is less than 5 so around the hundreds digit to previous 100 on
02:58the number line the previous 100 in case of 345 is 300 so 345 will be rounded
03:08down to 300 in the next number the 10 digit is 7 it is more than 5 so this
03:18number will be rounded up to the next 100 and next 100 in case of 572 is 600
03:27so 572 will be rounded up to 600 now our rounded off figures are 300 and 600
03:39adding them is quite easy 300 plus 600 gives 900 so our estimate for adding
03:50345 and 572 is 900 let's take another example we have to add 1200 and 3689 we
04:07have to make a quick estimate rather than actually adding these numbers by
04:12rounding off these numbers to the nearest 1000 for rounding off numbers to
04:19the nearest 1000 we see the hundreds digit if it's less than 5 we round it
04:26down that is the previous 1000 and if it's greater than equal to 5 we round it
04:34up that is to the next thousand here 2 is less than 5 so round the thousands
04:41digit to the previous thousand on the number line so we will be rounding off
04:47it to 1,000 6 is greater than 5 so round the thousands digit to the next
04:58thousand that is the 4,000 so our rounded off numbers are 1,000 and 4,000
05:09adding them is easy adding 1,000 and 4,000 we get 5,000 so estimate for
05:19adding 1,200 and 3,689 is 5,000 now let's take another example we have to
05:34subtract 42 from 689 we have to make a quick estimate rather than actually
05:44subtracting these numbers let's round off these numbers to the nearest 10 to
05:51make a quick estimate for rounding off numbers to the nearest 10 we see the
05:58ones digit if it's less than 5 we round it down that is to the previous 10 if
06:06it's 5 or above we round it up that is to the next 10 9 is greater than 5 so
06:16round it up to the next 10 that is to the next 10 so round it to 690 2 is less
06:26than 5 so round its tens digit to the previous 10 on the number line so round
06:33it down to 40 so rounded off figures to the nearest 10 are 690 and 40
06:43subtracting them is simpler 690 minus 40 will be 650 so the estimate for
06:55subtracting 42 from 689 is 650 now you may go ahead and take a quiz to learn
07:05more bye-bye