Tag: finding percentage of a number

Quizzes (0) Questions (48)

Questions Related to finding percentage of a number

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

They forecast 20 mm of rain, but we really got 25 mm. Find the error in percentage.

  1. $-20\%$
  2. $-10\%$
  3. $10\%$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\dfrac{Approximate Value - Exact Value}{Exact \  Value} \times100$
$\dfrac{20-25}{25} \times 100$ = $\dfrac{-5}{25} \times 100$
$\dfrac{-100}{5}$ = $-20$
Percentage of error $ = - 20\%$.

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

By evaluating $\dfrac{2.8^3\times 1.2^2}{0.56+3.78}$, closest estimate answer is:

  1. $7$
  2. $70$
  3. $0.7$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We need to evaluate $\dfrac{2.8^3 \times 1.2^2}{0.56+3.78}$

$\Rightarrow$  $\dfrac{3^3 \times 1.44}{4.34}$    $[\because\,\, 2.8\approx 3]$
$\Rightarrow$  $\dfrac{27\times 1}{4}$     $[\because\,\, 1.44\approx 1\,\text{and}\,\,4.34\approx 4]$
$\Rightarrow$  $6.75\approx 7.$
Therefore, $\dfrac{2.8^3\times 1.2^2}{0.56+3.78}=7$

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

Pankaj expected to earn $425 in a week. In fact he earned $500. What was the percentage error?

  1. $25\%$
  2. $15\%$
  3. $11.5\%$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\Rightarrow$  Here, Approximate value is $\$425$.

$\Rightarrow$  Exact value is $\$500$.
$\Rightarrow$  $\%\,Error=\dfrac{|Approximate\,value-Exact\,value|}{|Exact\,value|}\times 100$

$\Rightarrow$  $\%\,Error=\dfrac{|425-500|}{|500|}\times 100$

$\Rightarrow$  $\%\,Error=\dfrac{|-75|}{500}\times 100=15\%$

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

I estimated that the repairs to my car would cost $80. In fact they cost $120. What was the percentage error?

  1. $33.3 \%$
  2. $30.3 \%$
  3. $31.3 \%$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\dfrac{Approximate Value - Exact Value}{Exact \  Value} \times100$


$\dfrac{80-120}{120} \times 100$ = $\dfrac{40}{120} \times 100$'

$\dfrac{100}{3}$ = $33.3$


Percentage of error $ = 33.3\%$.
Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

Ritika expected to get $50 for her birthday, but she only got $35. What was the percentage error?

  1. $45.9\%$
  2. $32.8\%$
  3. $42.9\%$

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\dfrac{Approximate Value - Exact Value}{Exact Value} \times100$


$\dfrac{50-35}{35} \times 100$ = $\dfrac{15}{35} \times 100$
$\dfrac{1500}{35}$ = $42.9$
percentage of error $42.9$.

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

Susan tries to read 50 pages of her book every day.  One week (7 days) she only managed to read 280 pages. What was the percentage error?

  1. $25\%$
  2. $15\%$
  3. $2.5\%$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\Rightarrow$  Here, Approximate value of pages for one week = $50\times 7=350$

$\Rightarrow$  Exact value is $280$
$\Rightarrow$  $\%\,Error=\dfrac{|Approximate\,value-Exact\,value|}{|Exact\,value|}\times 100$

$\Rightarrow$  $\%\,Error=\dfrac{|350-280|}{280}\times 100$

$\Rightarrow$  $\%\,Error=\dfrac{70}{280}\times 100=25\%$

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

What is the percent error in using $3.14$ as an approximation for $\pi$ (which is $3.14159265358979323846$...) ?

  1. $0.5\%$
  2. $0.05\%$
  3. $0.005\%$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\Rightarrow$   Here Approximate value of $\pi$ is $3.14$.

$\Rightarrow$   Exact value of $\pi$ is $3.141592$

$\Rightarrow$   $\%\,Error=\dfrac{|Approximate\,valu-Exact\,value|}{|Exact\,value|}\times 100$

$\Rightarrow$  $\%\,Error=\dfrac{|3.14-3.141592|}{|3.141592|}\times 100$
$\Rightarrow$   $\%Error=0.05\%$

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

Estimated value of square root of $650$ is

  1. $25.495$
  2. $24.495$
  3. $2.5495$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\Rightarrow$   Here we have to find square root of $650$

$\Rightarrow$  $\sqrt{650}=\sqrt{25\times 26}$
$\Rightarrow$  $\sqrt{650}=5\sqrt{26}$
$\Rightarrow$  $\sqrt{650}=5\times  5.09$
$\Rightarrow$  $\sqrt{650}=25.495$

Multiple choice maths calculating and mental strategies 3 finding percentage of a number how many in all? problems on percentage

In an examination where full marks were $1000$, A gets $20\%$ more than B, B gets $20\%$ more than C, and C gets $15\%$ less than D. If A got $400$, what percentage of full marks did D get approximately ?

  1. $30\%$
  2. $35\%$
  3. $40\%$
  4. $45\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Full marks$=1000$

Let assume D got $x\%$ marks

 according to the question
 $C=85\%\times x=0.85x$
 $B=120\%\times 0.85x=1.02x$
 $A=120\%\times 1.02x=1.224x$
Now $A=400$

$1.224x=400$
$\implies x=327$
$\therefore$ percent of $D=(327/1000)\times 100=32.7\%\approx35\%$