West Bengal Board Solutions for Chapter: Time and Work, Exercise 7: Let's work out 17.2

There are two pipes for taking water from the municipality water tank. The tank can be emptied in $4$ hours by the two pipes separately. If both the pipes remain opened, let's calculate when the full tank will be emptied.

Ruma and Rohit can complete a work in $20$ days, Rohit and Sobha can complete that work in $15$ days. Ruma and Sobha can complete that work in $20$ days. Let's calculate how many days they will complete the work together. 

Alok, Kalam and Joseph individually can complete a work in $10,12\text{ and} 15$ days respectively. They started doing the work together. After $3$ days Kalam had to go. Let's calculate in how many days Alok and Joseph will complete the remaining work.

Mary and David can do a work individually in $10 \text{days}, 15 \text{days}$ respectively. At first mary alone worked for  $4$ days, then David alone worked for $5$ days and left. Maria came and completed the remaining work in $4$ days. If Mary, David and Maria would work together, let's calculate in how many days they would complete the work.

A municipality made a tank for water preservation and added pumps with it. The pumps separately can fill the empty tank in $15,20 \text{and} 30$ hours respectively. Today when the $3$ pumps started together at $7 \mathrm{am}$, $\frac{2}{3}$ part of the tank was filled with water. After $1$ hour the first pump and after $2$ more hours the third pump was stopped. Let's calculate when the tank was totally filled up.

A municipality made a tank for water preservation and added pumps with it. The pumps separately can fill the empty tank in $15,20 \text{and} 30$ hours respectively. Today when the $3$ pumps started together at $7 \mathrm{am}$, $\frac{2}{3}$ part of the tank was filled with water. After $1$ hour the first pump and after $2$ more hours the third pump was stopped. Let's calculate when the tank was totally filled up. Let's calculate how much of the tank the second pump filled up.

A municipality made a tank for water preservation and added pumps with it. The pumps separately can fill the empty tank in $15,20 \text{and} 30$ hours respectively. Today when the $3$ pumps started together at $7 \mathrm{am}$, $\frac{2}{3}$ part of the tank was filled with water. After $1$ hour the first pump and after $2$ more hours the third pump was stopped. Let's calculate when the tank was totally filled up. Let's calculate how much of the tank the second pump filled up.  When the third pump is stopped, let's calculate how much of the tank was filled with water.

My friend and Rina can do garden work alone in $4$ hours. I can do that work alone in $2$ hours. But if we do that work together, let's calculate how much time will be needed.