Best way is this.
1) Get the unit of quantity of work. Make it a number which you find LCM of the given digits.
2) Calculate the rate of work for each person.
And then calculate what is asked.
So as per above,
Lets assume that 20*12=240 unit of work is there.
Assume rate of work per day for Matt is m, and for Peter is p;
Matt and Peter can do together a piece of work in 20 days. implies..
Now, peter works for 22 day while, matt works for 12 days.
Solving the equations, we find the value of m and p as 2.4, and 9.6 unit of work/day respectively.
So peter will take, 240/9.6=25 days.
Matt and Peter can do together a piece of work in 20 days. After they have worked together for 12 days Matt stops and Peter completes the remaining work in 10 days. In how many days Peter complete the work separately.
What is the best way to solve these problems?