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Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

Simplify : $\displaystyle \frac{3.6\times 0.48\times 2.50}{0.12\times 0.09\times 0.5}$

  1. 80

  2. 800

  3. 8000

  4. 80,000
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle \frac{3.6\times 0.48\times 2.50}{0.12\times 0.09\times 0.5}=\frac{36\times 48\times 250}{12\times 9\times 5}=800 $


No of decimal places in num and den being equal

Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

Which number is equal to
$\left ( \displaystyle \frac {0.1}{0.01}\, +\, \displaystyle \frac {0.01}{0.1} \right )\, ?$

  1. $10.1$
  2. $1.10$
  3. $1.01$
  4. $10.01$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let us first write the decimals as fractions as follows:


$0.1=\dfrac { 1 }{ 10 } \ 0.01=\dfrac { 1 }{ 100 }$ 

Now, the given expression $\dfrac { 0.1 }{ 0.01 } +\dfrac { 0.01 }{ 0.1 }$ can be solved as follows:
 
$\dfrac { 0.1 }{ 0.01 } +\dfrac { 0.01 }{ 0.1 } =\dfrac { \dfrac { 1 }{ 10 }  }{ \dfrac { 1 }{ 100 }  } +\dfrac { \dfrac { 1 }{ 100 }  }{ \dfrac { 1 }{ 10 }  } =\dfrac { \dfrac { 1 }{ 1 }  }{ \dfrac { 1 }{ 10 }  } +\dfrac { \dfrac { 1 }{ 10 }  }{ \dfrac { 1 }{ 1 }  } =10+\dfrac { 1 }{ 10 } =\dfrac { (10\times 10)+1 }{ 10 } =\dfrac { 100+1 }{ 10 } =\dfrac { 101 }{ 10 } =10.1$

Hence, $\dfrac { 0.1 }{ 0.01 } +\dfrac { 0.01 }{ 0.1 }=10.1$

Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

Simplify : $\displaystyle \frac{0.2\times0.2+0.2\times0.02}{0.044}$

  1. $0.4$
  2. $0.2$
  3. $0.1$
  4. $1$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

We will first convert the decimals into fraction in the given fraction and then solve it as follows:


$\dfrac { 0.2\times 0.2+0.2\times 0.02 }{ 0.044 } =\dfrac { \left( \dfrac { 2 }{ 10 } \times \dfrac { 2 }{ 10 }  \right) +\left( \dfrac { 2 }{ 10 } \times \dfrac { 2 }{ 100 }  \right)  }{ \dfrac { 44 }{ 1000 }  } =\dfrac { \dfrac { 4 }{ 100 } +\dfrac { 4 }{ 1000 }  }{ \dfrac { 44 }{ 1000 }  } =\dfrac { \dfrac { 40+4 }{ 1000 }  }{ \dfrac { 44 }{ 1000 }  } =\dfrac { \dfrac { 44 }{ 1000 }  }{ \dfrac { 44 }{ 1000 }  } =1$

Hence, $\dfrac { 0.2\times 0.2+0.2\times 0.02 }{ 0.044 } =1$

Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

Evaluate the square root of $\displaystyle \frac{0.342\times 0.684}{0.000342\times 0.000171}$.

  1. $1000$
  2. $1500$
  3. $2000$
  4. $2500$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Consider the given fraction $\dfrac { 0.342\times 0.684 }{ 0.000342\times 0.000171 }$ and find the square root as follows:

 
$\sqrt { \dfrac { 0.342\times 0.684 }{ 0.000342\times 0.000171 }  } \ =\sqrt { \dfrac { 342\times 684 }{ 342\times 171 } \times \dfrac { 1000000\times 1000000 }{ 1000\times 1000 }  } \quad \quad \quad \quad \quad \quad \quad \left{ \because \quad 0.1=\dfrac { 1 }{ 10 }  \right} \ =\sqrt { 4\times 1000000 } \ =\sqrt { 4000000 } \ =\sqrt { { \left( 2000 \right)  }^{ 2 } } \ =2000$

Hence, the square root of $\dfrac { 0.342\times 0.684 }{ 0.000342\times 0.000171 }$ is $2000$.

Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

A student was asked to simplify $\displaystyle \frac{0.6\times 0.6\times 0.6+0.5\times 0.5\times 0.5+0.1\times 0.1-0.09}{0.6\times 0.6+0.5\times 0.5+0.1\times 0.1-0.41}$ and his answer was 0.6 By what per cent was his answer wrong

  1. 25%

  2. 100%

  3. 50%

  4. 120%
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\displaystyle \frac{0.6\times 0.6\times 0.6+0.5\times 0.5\times

0.5+0.1\times 0.1-0.09}{0.6\times 0.6+0.5\times 0.5+0.1\times

0.1-0.41}$


$\dfrac{0.216+0.125+0.01-0.09}{0.36+0.25+0.01-0.41}= \dfrac{0.261}{0.21} = 1.2$

Student got answer as $0.6$

Hence His Answer was wrong with $\dfrac{0.6}{1.2}\times 100= 50$%

Multiple choice maths calculations and mental strategies 4 mental additions and subtractions of decimals multiplication and division of decimals mental multiplication and division

If x and y are positive numbers such that x + y = 1, which of the following could be the value of 100x + 200y?
I. 80
II. 140
III. 199

  1. II only

  2. III only

  3. I and II

  4. I and III

  5. II and III
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Given x+y=1  So 100x+100y=100 and 200x+200y =200

So       100 < 100x + 200y <200
II and III satisfies this situation So correct answer will be Option E