Tag: multiplying decimals

Quizzes (0) Questions (49)

Questions Related to multiplying decimals

Multiple choice maths decimal fraction multiplying decimals multiplication of decimals multiplication of division of decimal fraction by whole number and decimal fraction

(Three rupees $5$ paise) $\times$ (five rupees $40$ paise) is equal to

  1. $Rs. 18.90$
  2. $Rs. 16.47$
  3. $Rs. 17.64$
  4. $RS. 15.37$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know that 100 paise is nothing but 1 Rupee.

So $5Paise =  0.05 Rupees$
Also $40 Paise = 0.4 Rupees$
Now Three Rupees $5 Paise = 3 Rupees + 0.05 Rupees$
                                               $=3.05 Rupees$
Also Five Rupees $40 Paise= 5 Rupees + 0.40 Rupees$
                                              $= 5.40 Rupees$
Now to find $(Three\quad rupees\quad 5paise)×(fiverupees\quad 40paise)$
$3.05\times 5.40 = 16.47$

Multiple choice maths decimal fraction multiplying decimals multiplication of decimals multiplication of division of decimal fraction by whole number and decimal fraction

Using  identity the value obtained from the product $25.4 \times 24.6$ is

  1. $624.84$
  2. $642.84$
  3. $264.84$
  4. $62.84$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation


Given

$25.4\times24.6$

we can re-wright them as

$(25+0.4)\times (25-0.4)$

$\because \ we \ have \ an\ identity \ (a+b) (a-b)=a^2-b^2$

$a=25,\ b=0.4$


$= (25)^2-(0.4)^2$

$= 625- 0.16$

$=624.84$

$\therefore option\ A\ is\ correct.$


Multiple choice maths decimal fraction multiplying decimals multiplication of decimals multiplication of division of decimal fraction by whole number and decimal fraction

Without actual multiplication, the value $79.01 \times 79.01 + 2 \times 79.01 \times 20.99 + 20.99 \times 20.99$

  1. $10,009$
  2. $1000.06$
  3. $10,000$
  4. $1007$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$79.01\times 79.01+2\times 79.01\times 20.99+20.99\times 20.99....(1)$
$\dfrac {7901}{100}\times \dfrac {7901}{100}+2\times \dfrac {7901}{100}\times  \dfrac {2099}{100}+\dfrac {2099}{100}\times \dfrac {2099}{100}....(2)$

$7901\times 7901=(7901)^2 =(7900 +1)^2$    $\quad [\because \ 79^2=(80-1)^2\\ =80^2+1-2.80\\ =6400+1-160\\ =6241]$
$=(7900)^2 +1^2+2(7900)(1)$
$=62410000+1+15800$
$=62425801$ 

$2099\times 2099 =(2099)^2=(2100-1)^2$ $\quad [\because \ 21^2=(20+1)^2\\ =20^2+1+2.20\\ =400+40+1\\ =441]$
$=(2100)^2+1^2-2(2100)(1)$
$=4410000+1-4200$
$=4405801$

$7901\times 2099=(7900+1) (2100-1)$
$=(7900)(2100)-7900+2100-1$
$=16590000-7900+2100-1$
$=16584299\ =16584199$
from $(2)$
$\dfrac {62425801}{10000}+\dfrac {2\times 16584199}{10000}+\dfrac {4405801}{10000}$
$6242.5801+\dfrac {33168398}{10000}+440.5801$
$6242.5801+3316.8398+440.5801$
$=10,000$
Multiple choice maths decimal fraction multiplying decimals multiplication of decimals multiplication of division of decimal fraction by whole number and decimal fraction

Find the product
$\displaystyle 0.123\times 100$

  1. $1.23$
  2. $123$
  3. $12.3$
  4. $1230$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
To find $0.123\times 100$
Since, $100$ has $2$ zeros and $0.123$ has decimal point after $3$ digits
So, the product will have decimal point after $1$ digit from left

Therefore, value of $0.123\times 100$ is $12.3$.

Multiple choice maths decimal fraction multiplying decimals multiplication of decimals multiplication of division of decimal fraction by whole number and decimal fraction

Find the product
$\displaystyle 7.854\times 10$

  1. $785.4$
  2. $78.54$
  3. $7854$
  4. $78540$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
To find $7.854\times 10$
Since, $10$ has $1$ zero and $7.854$ has decimal point after $3$ digits
So, the product will have decimal point after $2$ digits from left

Therefore, value of $7.854\times 10$ is $78.54$.