A can complete a project in 20 days while B can complete same project in 30 days. If A and B start working together and A leaves the work 15 days before completion of project, then in how many days the project will be completed? Choose the correct choice from the following choices:
A) 18
B) 19
C) 20
D) 21
E) 22
A's 1day work=1/20;   B's 1day work=1/30;   (A+B) 1day work=(1/20+1/30)=1/12;   It is given that A leaves the work 15 days before completion of the project..   Thus,B alone does the remaining job in 15 days.   So,In 15 days ,B can do 1/2 w ..   Thus,(A+B) have worked (1-1/2)=1/2 w..   (A+B)can do 1/12 work in 1 day...   They did 1/2 w in 6 days.   Total days=(6+15)= 
<gadget id="calculator">(6+15)</gadget>
<output>21</output>
21   ANSWER:21
<result>D</result>
A can complete a project in 20 days while B can complete same project in 30 days. If A and B start working together and A leaves the work 15 days before completion of project, then in how many days the project will be completed?