2. Questions Bank
  3. 8th Class
  4. Mathematics
  5. Direct and Inverse Proportions

8th Class Mathematics Direct and Inverse Proportions Question Bank Direct & Inverse Proportional (Time & Work)

  • question_answer
    Two pipes A and B can fill a tank in 24 min. and 32 minutes respectively. If both the pipes are opened together, after how much time B should be closed so that the tank is full in 18 minutes.

    A)  7 minutes                     

    B)  6 minutes        

    C)  8 minutes  

    D)  9 minutes

    Correct Answer: C

    Solution :

    (c): Let after 't' minutes 'B' be closed For first 't' minutes Part filled\[=t*\left[ \frac{1}{24}+\frac{1}{32} \right]\] \[=t*\frac{7}{96}\] Part left \[=\left( 1-\frac{7t}{96} \right)\] 'A' filled 1/24 part in 1 min \[\Rightarrow \]A fills \[=\left( 1-\frac{7t}{96} \right)\] part in 24\[=\left( 1-\frac{7t}{96} \right)\] min Now, \[t+24\text{ }\left( 1-\frac{7t}{96} \right)=18\] \[\Rightarrow t+24-\frac{7t}{4}=8\] \[\Rightarrow 6=\frac{3t}{4}\Rightarrow t=18\].


You need to login to perform this action.
You will be redirected in 3 sec spinner