Question

Estimate each of the following using the general rule:
a.730 + 998
b.796 – 314
c.12904 + 2888
d.28292 – 21496

Answer 1

Hint: Firstly, round off the individual values to 100s or 1000s respectively.
Then, find the sum or difference of the rounded off numbers.
Thus, write the required sum or difference.

Complete step-by-step answer:
(a) The estimated value of 730 by rounding it off will be 700.
      The estimated value of 998 by rounding it off will be 1000.
      So, the estimated value of \[730 + 998 = 700 + 1000 = 1700\] .
(b) The estimated value of 796 by rounding it off will be 800.
      The estimated value of 314 by rounding it off will be 300.
      So, the estimated value of \[796 - 314 = 800 - 300 = 500\] .
(c) The estimate value of 12904 by rounding it off will be 13000.
      The estimated value of 2888 by rounding it off will be 3000.
      So, the estimated value of \[12904 + 2888 = 13000 + 3000 = 16000\] .
(d) The estimate value of 28292 by rounding it off will be 28000.
      The estimated value of 21496 by rounding it off will be 21000.
      So, the estimated value of \[28292 - 21496 = 28000 - 21000 = 7000\] .

Note: Rounding off to nearest 10 (tens):
(i)If the units place digit of a 2-digit number is greater than 5, replace units place digit by 0 and add +1 to the tens place digit. If the units place digit of a 2-digit number is lesser than 5, just replace units place digit by 0 and write tens place digit as it is.
(ii).Rounding off to nearest 100 (hundreds):
If the last 2 place digits of a 3-digit number form a number greater than 50, replace the last two place digits by 0 and add +1 to the hundreds place digit. If the last two place digits of a 3-digit number form a number lesser than 50, just replace the last two place digits by 0 and write hundreds place digits as it is.
(iii).Rounding off to nearest 1000 (thousands):
If the last 3 place digits of a 4-digit number form a number greater than 500, replace the last three place digits by 0 and add +1 to the thousands place digit. If the last three place digits of a 4-digit number form a number lesser than 500, just replace the last three place digits by 0 and write thousands place digits as it is.