Tag: mental arithmetic

Questions Related to mental arithmetic

Round off to nearest lakhs: The given number is $38,65,62,048$

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $38,68,60,000$

  2. $38,65,600$

  3. $38,65,00,000$

  4. $38,66,00,000$

Show answer
Correct Option: D
Explanation:

To round of the given no in nearest lakh we need to see the value at ten thousand place which is $6$ it is more than $5$. 

So we round off lakhs digit to $5+1=6$
So we will round off. $38,65,62,048$ will become $38,66,00,000$

Round off  $231$ to nearest $100.$

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $200$

  2. $300$

  3. $250$

  4. $350$

Show answer
Correct Option: A
Explanation:

$\Rightarrow$  In number $231$,tens digit is $3$ 

$\Rightarrow$  Its tens digit is 3, which is less than 5. So, we replace each of the tens and ones digits by $0$ and keep the other digits as they are to round off the given number to nearest hundreds.
$\therefore$  Round of 231 to nearest 100 is $200$.

Round off $829$ to nearest $100$. 

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $800$

  2. $700$

  3. $900$

  4. $850$

Show answer
Correct Option: A
Explanation:

$\Rightarrow$  The given number is $829$

$\Rightarrow$  Its tens digit is $2$, which is less than $5$. 
$\Rightarrow$  So, we replace each of the tens and ones digits by $0$ and keep the other digits as they are to round off the given number to nearest $100.$
$\therefore$  Round off $829$ to nearest $100$ is $800$.

Round off $7065$ to nearest $1000$  :

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $700$

  2. $7000$

  3. $70$

  4. $7$

Show answer
Correct Option: B
Explanation:

Rounding off $7065$ to nearest $1000$ we check if $065$ is less than $500$ or not,

As $065 < 500$, we round it off to $000$

$\therefore 7065$ to nearest $1000$ equals $7000$

Round off  $63$ to nearest $10$ 

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $60$

  2. $70$

  3. $65$

  4. $63$

Show answer
Correct Option: A
Explanation:

Rounding off $63$ to nearest $10$ we check if $3$ is less than $5$ or not,

As $3 < 5$, we round it off to $0$

$\therefore 63$ to nearest $10$ equals $60$

Round off the following number to the nearest $10$ and $100$:
$1634$

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $1630,1600$

  2. $1640,1730$

  3. $1740,1700$

  4. $1640,1734$

Show answer
Correct Option: A
Explanation:
$1634=163.4 \times  10^1$

Rounding to nearest 10, we round off $163.4$ to $163.0$ as $4$ is less than $5$

Answer: $1630$

Similarly for 100 th position 
$1634 = 16.34\times 20^2$

$16.34 = 16.30 = 16.00$

So the answer is $1600$.

Round-off $76,890$ to nearest $10$.

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $76,890$

  2. $76,880$

  3. $76,900$

  4. $77,000$

Show answer
Correct Option: A
Explanation:

$\Rightarrow$   The given number is $76,890$.

$\Rightarrow$   In number 76890, its unit digit is $0$, which is already nearest to 10.
$\Rightarrow$  So, don't need to change anything.
$\therefore$   $76,890$ is nearest to 10.

Round-off $4353$ to nearest $100$.

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $4353$

  2. $4350$

  3. $4360$

  4. $4400$

Show answer
Correct Option: D
Explanation:

$\Rightarrow$  The given number is $4353$

$\Rightarrow$  In number 4353, its tens digit is 5, which is equal to 5. 
$\Rightarrow$  So, we increase the digits at hundreds place by 1 and replace each one of the digits at tens and ones place by 0 to round off the given number to nearest to 100.

$\therefore$   The number becomes $4400$

Round-off $52,398$ to nearest $1000$.

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $52,390$

  2. $52,400$

  3. $52,000$

  4. $53,000$

Show answer
Correct Option: C
Explanation:

$\Rightarrow$  The given number is $52,398$

$\Rightarrow$  In number $52398$, its hundred digit is $3$, which is less than $5$. 
$\Rightarrow$  So, we replace each one of the digits at hundreds, tens and ones place by $0$ to round off the given number to nearest to $1000$.

$\therefore$   The number becomes $52,000$

Round-off $3789$ to nearest $100$

maths mental arithmetic estimation and rounding off estimations, bounds and rounding off rounding off numbers rounding of decimals

  1. $3789$

  2. $3790$

  3. $3800$

  4. $4000$

Show answer
Correct Option: C
Explanation:

$\Rightarrow$  The given number is $3789$

$\Rightarrow$  In number 3789, its tens digit is 8, which is greater than 5. 
$\Rightarrow$  So, we increase the digits at hundreds place by 1 and replace each one of the digits at tens and ones place by 0 to round off the given number to nearest to 100.

$\therefore$   The number becomes $3800$