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Questions Related to multiplication methods

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

If $\displaystyle \left ( 1^{2}+2^{2}+3^{2}+...+10^{2} \right )=385$ then the value of $\displaystyle \left ( 2^{2}+4^{2}+6^{2}+...+20^{2} \right )$

  1. 770

  2. 1155

  3. 1540

  4. (385 x 385)

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\left(2^2 + 4^2 + 6^2 + ... + 20^2\right) = \left(1 \times 2\right)^2 + \left(2\times 2\right)^2 + \left(2 \times 3\right)^2 + ... + \left(2 \times 10\right)^2$



$= \left(2^2 \times 1^2\right) + \left(2^2 \times 2^2\right) + \left(2^2 \times 3^2\right) + ... + \left(2^2 \times 10^2\right)$

$= 2^2 \times \left [1^2 + 2^2 + 3^2 + ... + 10^2\right]$

$\left(1^2+2^2+3^2+....+n^2\right) = \frac{1}{6}n\left(n+1\right)\left(2n+1\right)$

$=\left(4\times\frac{1}{6}\times 10\times 11\times 21\right)$

$=\left(4\times 5\times 77\right)$

$= 1540$

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

When Sholey screened on the TV there was a commercial break of 5 min after every 15 min of the movie If from the start of the movie to the end of the movie there was in all 60 min of commercials that was screened what is the duration the movie?

  1. 180 min

  2. 195 min

  3. 169 min

  4. 165 min

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In every 15 min there was a break of 5 min
If total 60 min break in all movie then number of commercial break =$\frac{60}{5}=12$
If 12 breaks are in movie then the duration of movie=$12\times 15+15=195    minutes$

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

Simplify $(9^{4/3} \div 27^{2/3}) \times 3^{3/2}$

  1. $3^{9/5}$
  2. $3^{13/6}$
  3. $3^{37/6}$
  4. None of these

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle \left ( \left ( 3^2 \right )^{4/3} \div \left ( 3^3 \right )^{2/3} \right ) \times 3^{3/2}$
$= 3^{8/3} \div 3^2 \times 3^{3/2}$
$= \displaystyle 3^{8/3 - 2 + 3/2} $
$= \displaystyle  3^{ \displaystyle \frac{16 - 12 + 9}{6}}$
$= 3^{13/ 6}$

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

The product of two numbers is 0.008 and one is $\displaystyle \frac{1}{5}$ of the other, then the smaller number is

  1. 0.002

  2. 0.004

  3. 0.2

  4. 0.04

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the smaller number is x 

Then bigger number  of is 5 times of smaller number because one number is $\frac{1}{5}$ another
Then product of number =$5x\times x=0.008$
$\Rightarrow x^{2}=0.0016$
$\Rightarrow x=0.04$ 

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

On dividing 4996 by a certain number the quotient is 62 and the the remainder is 36 what is the divisor ? 

  1. 80

  2. 85

  3. 90

  4. 95

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the divisor number is x

Then$ quotient \times divisor +reminder =number$
$\therefore 62x+36=4996$
$\Rightarrow 62x=4996-36$
$\Rightarrow 62x=4960$
$\Rightarrow x=80$
Then divisor is 80

Multiple choice maths ways to multiply and divide mental multiplication multiplication methods multiplication of numbers

A boy was asked to multiply a certain number by 25 He multiplied it by 52 and got his answer more by 324 than the correct answer The number to be multiplied was

  1. 15

  2. 12

  3. 18

  4. 23

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the number is x

The if be multiply by 25 then correct answer =25x 
But boy multiply with 52 then boys answer =52 x
As per question boy answer if more then 324 than correct answer 
$\therefore 52x=25x+324$
$\Rightarrow 52x-25x=324$
$\Rightarrow 27x=324$
$\Rightarrow x=12$