Question 1163735
<br>
There are many ways to solve the problem using formal algebra; the other tutor showed one good way.<br>
If a formal algebraic solution is not required, I like to encourage students to solve the problem informally with logical reasoning and mental arithmetic.  The mental exercise you get by THINKING your way through the problem will be good for you.<br>
A alone can do the whole job in 20 days.  So when A and B together complete the job in 12 days, the fraction of the job that A does is 12/20 = 3/5.<br>
That means in 12 days B does 2/5 of the job.<br>
A working alone for 16 days will complete 16/20 = 4/5 of the job; 1/5 of the job will remain to be done.<br>
Since B can do 2/5 of the job in 12 days, he can do 1/5 of the job in 6 days.<br>
ANSWER: B will take 6 days to finish the job.<br>