Tag: rule of three

Questions Related to rule of three

A car takes 2 hours to reach a destination by travelling at the speed of 60 km/h. when the car travels at the speed of 80 km/h it takes 

maths rule of three inverse proportion direct proportion and inverse proportion types of proportions

  1. one and half hour

  2. one hour

  3. two hour

  4. None

Show answer
Correct Option: A
Explanation:

Let the car takes x hours to reach a destination by travelling at the speed of 80 km/h. Then,

Speed (in km/hr) 60 80
Time (in hours) 2 x

Clearly, more the speed, less will be the time taken. So, it is a case of inverse proportion.
$ \therefore \,\,\, 60 \times 2 = 80 \times x  \Rightarrow x = \displaystyle \frac{60 \times 2}{80} = \frac{3}{2}$
Hence, the time taken will be $\displaystyle 1\frac{1}{2}$ hours.

Which is an example of inverse proportion?

maths rule of three inverse proportion direct proportion and inverse proportion types of proportions

  1. More amount of sweets, more total cost

  2. More length of cloth, more cost

  3. More expenditure, less saving

  4. More height of object, more length of its shadow

Show answer
Correct Option: C
Explanation:

2 quantities say it be $x , y$ are said to be in proportion when the change in value of $x$ , leads to the equal change in value of $y$.

If $x$ increases and hence  $y$ decreases proportionally, it is called Inverse proportion i.e $x\propto\dfrac{1}{y}$
For example, In option C, if our expenses are more, then we are left with lesser savings from a fixed salary or income.
hence, Expenditure and savings are in inverse proportion.
So the answer is C

Which is example of inverse proportion?

maths rule of three inverse proportion direct proportion and inverse proportion types of proportions

  1. Length of edge of square & its area

  2. Speed and time taken

  3. Length of edge of square & its perimeter

  4. Quantity of pencils & total cost

Show answer
Correct Option: B
Explanation:

2 quantities say it be $x , y$ are said to be in inverse proportion when the increse in value of $x$ , leads to the decrease in value of $y$.


we know that,
$speed = \dfrac{distance}{time}$

i.e., Speed is directly proportion to distance and at a fixed distance  inverse proportion to time.

Hence at fixed distance, if speed increses, time taken will decrease and vice versa. which is Option B

A car travels $40\ kms$ in $30$ mins. If the speed of bus remains same, how far can it travel in $3$ hrs?

maths rule of three inverse proportion direct proportion and inverse proportion types of proportions

  1. $120\ km$

  2. $80\ km$

  3. $240\ km$

  4. None of these

Show answer
Correct Option: C
Explanation:
A car travels $40$ kms in $30$ mins
Let $x$ be the distance covered by a bus in $3$ hrs $=180$ mins
Then, $\dfrac {40}{30} = \dfrac {x}{180}$

$\Rightarrow x = \dfrac {40\times 180}{30} = 240\ km$.

The number of workers increased the days to complete the work decreased."is example of 

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. Inverse ratio

  2. Direct ratio

  3. Both of A and B

  4. none of above

Show answer
Correct Option: A
Explanation:

Inverse proportion is a relation between two quantities such that one increases in proportion as the other decreases i.e. If $x$ increases as $y$ decreases, $x \alpha \dfrac{1}{y}$ 

In the given example, if the no. of workers are increased then the time required to do the job will decrease, likewise if no. of workers decrease, then time to do the same job will increase i.e. no. of workers and time to do job are inversely proportional to each other.
hence the answer is inverse proportion
So, the answer is option A.

Four angles of a quadrilateral are in the ratio $3:5:7:9$. The greatest angle is _________.

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. $125^o$

  2. $75^o$

  3. $135^o$

  4. $120^o$

Show answer
Correct Option: C
Explanation:
Let the angles of quadrilateral be $x,y,z,w.$
 
Given ,$x:y:z:w=3:5:7:9$

$x=3k$
$y=5k$
$z=7k$
$w=9k$

we k.n.t sum of angles of a quadrilateral is $360^{\circ }$
$x+y+z+w=3k+5k+7k+9k=360^{\circ }$
$\Rightarrow 24k=360^{\circ }$
$\Rightarrow k=\dfrac{360^{\circ }}{24}=15^{\circ }$

Greatest angle is $w=9k=9(15^{\circ })=135^{\circ }$

A stone is dropped into a well and the report of the stone striking the bottom is heard $7.7$ seconds after it is dropped. Assume that the stone falls $16t^2m$ in t seconds and that the velocity of sound is $1,120$  per second. The depth of the well is:

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. $784$m

  2. $342$m

  3. $1568$m

  4. $156.8$m

  5. none of these

Show answer
Correct Option: A
Explanation:

Since the distance d travelled by the stone and the sound is the same,

 $d = r _1t _1 = r _2t _2$.
 $\therefore$ The times of travel are inversely proportional to the rates of fail: 
$r _1/r _2 = t _2/t _1$,
$\therefore \dfrac{16t^2/t}{1120} = \dfrac{7.7-t}{t}; $
 $\therefore t = 7 (seconds);$
$ \therefore 16t^2 = 16\times 7^2 = 784 (metre)$.

A farmer has enough food to feed $28$ animals in his cattle for 9 days. How long would the food last if there were $8$ more animals in his cattle ?

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. $5$

  2. $7$

  3. $10$

  4. None of these

Show answer
Correct Option: B
Explanation:
let say each animal eat $x$ amount of food per day
$\rightarrow$ Amount of food eaten by $28$ animal for $1$ day
$=28 \times x$
$\rightarrow$ Amount of food required for $28$ animal for $9$ days
$=28 x \times 9$
$=(28 \times 9)x \ 252x$
$\therefore$ The farmer has $252x$ amount of food.
now, the number if animal $=28+8=36$.
$\boxed{No. of\ days\ the\ food\ will\ last = \dfrac{amount\ of\ food}{food\ required\ for\ 1\ day}}........1$
food required for $1$ day $=(no.of\ animals) \times x$
food requires for $1$ day $=36x $ (put\ this\ in\ $1$)
No. o days food will last $=\dfrac{252x}{36x}= \dfrac{252}{36}=7$
$\boxed{\because The\ food\ last\ for\ 7\ days\ if\ 8\ animals\ are\ added}$  

































Mark the correct alternative of the following.
If six men can do a piece of work in $6$ days, then $3$ men can do same work in?

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. $10$ days

  2. $12$ days

  3. $15$ days

  4. $18$ days

Show answer
Correct Option: B
Explanation:

Work done by $6 = $ work done by $3$


$6 \times 6 = 3 \times x$


$x = \dfrac{36}{3}$

$x = 12 $ days

Ten men, working for 6 days of 10 hours each, finish $ \dfrac {5}{21} $ of a piece of work. How many men working at the same rate and for the same number of hours each day, will be required to complete the remaining work in 8 days?

maths direct proportion and inverse proportion inverse proportion rule of three types of proportions

  1. 24

  2. 26

  3. 25

  4. 21

Show answer
Correct Option: A
Explanation:

Lets first find the number of working hours required to complete $\dfrac { 5 }{ 21 }$ of the work.
M = number of men
D = number of days
H = number of hours worked per day
N = work done
MDH = N
10$\times $6$\times $10 = $\dfrac { 5 }{ 21 }$
600 hours to complete $\dfrac { 5 }{ 21 }$ of work
Let the total number of hours required to complete the work be $x$ then
$x$ = $\dfrac { 5 }{ 21 }$ $\div $600
   = 600$\times $$\dfrac { 21 }{ 5
 }$
$x$   = 2520 hours
so the remaining work is $x$$-$  $\dfrac { 5 }{ 21 }$
               = $\dfrac {16 }{ 21 }$ $x$

               =$\dfrac {16 }{ 21 }$$\times $2520
               = 1920 hours required to complete remaining $\dfrac {16 }{ 21 }$ of the work
 now the equation we get is
MDH = N
MDH = 1920
M $\times $ 8$\times $10 = 1920
M =  $\dfrac { 1920 }{ 80 } $
M = 24
 Ans. 24 men