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 20 days before completion of project, then in how many days the project will be completed?  Select the correct option:
A) 18 B) 19 C) 20 D) 21 E) 24
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 20 days before completion of the project..   Thus,B alone does the remaining job in 20 days.   So,In 20 days ,B can do 2/3 w ..   Thus,(A+B) have worked (1-2/3)=1/3 w..   (A+B)can do 1/12 work in 1 day...   They did 1/3 w in 4 days.   Total days=(4+20)= 
<gadget id="calculator">(4+20)</gadget>
<output>24</output>
24   ANSW24R:24
<result>E</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 20 days before completion of project, then in how many days the project will be completed?