Page 15 - Maths Class 06

5. Round off 836 to the near est hundred.
836

400 500 600 700 800 900 1000
836 ¾® 800
836 is closer to 800 than to 900. So, 836 is rounded off downwards to 800.

6. Round off 6500 to the nearest thousand.
6500

2000 3000 4000 5000 6000 7000
6500 ¾® 7000

6500 is halfway between 6000 and 7000. So, 6500 is rounded off upwards to 7000.
We now give a procedure for quick rounding off the numbers:

For rounding off a number to the nearest ten,
We look at the digit in the ones place. It it is 0, 1, 2, 3 or 4 we replace it by zero (0). If the digit in the ones
place is 5, 6, 7, 8 or 9, we replace it by zero (0) and also increase the digit in the place by 1.

For rounding off a number to the nearest hundred,
We look at the digit in the tens place. If it is 0, 1, 2, 3 or 4 we replace the digit in the tens and ones places
by zeros (00). If the digit in the tens place is 5, 6, 7, 8 or 9, we replace the digits in the tens and ones place
by zeros and also increase the digit in the hundreds place by 1.

For rounding off a number to the nearest thousand,
We look at the digit in the hundreds place. If it is 0, 1, 2, 3 or 4 we replace the digits in the hundreds, tens
and ones places by zeros (000). If the digit in the hundreds place is 5, 6, 7, 8 or 9, we replace the digits in
the hundreds, tens and ones places by zero (000) and also increase the digit in the thousands place by 1.
For rounding off a number to the nearest ten thousand,

We look at the digit in the thousands place. If it is 0, 1, 2, 3 or 4 we replace the digits in the thousands
hundreds, tens and ones places by zeros (0000). If the digit in the thousands place is 5, 6, 7, 8 or 9, we
replace the digits in the thousands, hundreds, tens and ones places by zeros (0000) and also increase the
digit in the ten thousands place by 1.

Estimating Sum, Difference, Product or Quotient
To estimate the answers involving the basic operations ( . .,i e +, –, ´ and ¸). We first round off numbers to
the nearest, hundred or thousand as required in the questions and them perform the operations.
EXAM PLE 1. Esti mate the sum (93 + 77) to the near est ten.

SOLU TION : 93 is approx i mated to 90 [ Q ones digit i e. ., 4 5< ]
77 is approx i mated to 80 [ Q ones digit i e. ., 9 > 5]

\ 93 77+ = 90 + 80 = 170

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