L Mohan Lal Solutions for Exercise 1: PREVIOUS QUESTIONS

$A$ can do a piece of work in $12$ days and $B$ can do the same work in $18$ days. If $A$ works for three days, then how many days will the remaining work be completed by $B$?

A student can solve $75$ questions in one hour. Another student can solve $100$ questions in two hours. In how many minutes do they together solve $250$ questions?

$A$ and $B$ can do work in $72$ days. $B$ and $C$ in $120$ days. $A$ and $C$ in $90$ days. In how many days can $A,B,C$ together do the work?

$3$ pumps working $8$ hours a day, can empty a tank in $2$ days. How many hours a day must $4$ pumps work to empty the tank in $1$ day?

$A$ and $B$ can do a piece of work in $5$ days. $B$ and $C$ can do the same piece of work in $7$ days. $A$ and $C$ can do it in $4$ days. What is the time required for $A$ to complete the work if he works alone (in days)?

If a boat goes $7km$ upstream in $42$ minutes and the speed of the stream is $3kmph$, then the speed of the boat in still water is (in $kmph$)?

$X$ and $Y$ can do a piece of work in $15$ days and $10$ days respectively. They work for $3$ days after which $X$ was replaced by $Z$. If the work was finished in the next $4$ days, find the number of days in which $Z$ alone could do the work (in days)?

$2$ men and $7$ boys can do a piece of work in $14$ days, $3$ men and $8$ boys can do the same in $11$ days. $8$ men and $6$ boys can do three times the amount of this work in how many days?