P and Q can do a work in 30 days. Q and R can do the same work in 24 days and R and P in 20 days. They started the work together, but Q and R left after 10 days. How many days more will P take to finish the work?  Select:
A) 10  B) 15  C) 18  D) 22  E) 25
Explanation :   Let work done by P in 1 day = p,   Work done by Q in 1 day = q,   Work done by R in 1 day = r   p + q = 1/30   q + r = 1/24   r + p = 1/20   Adding all the above, 2p + 2q + 2r = 1/30 + 1/24+ 1/20 = 15/120 = 1/8   =&gt; p + q + r = 1/16   =&gt; Work done by P,Q and R in 1 day = 1/16   Work done by P, Q and R in 10 days = 10 × (1/16) = 10/16 = 5/8   Remaining work = 1 = 5/8 = 3/8   Work done by P in 1 day = Work done by P,Q and R in 1 day - Work done by Q and R in 1 day   = 1/16 – 1/24 = 1/48   Number of days P needs to work to complete the remaining work = (3/8) / (1/48)= 
<gadget id="calculator">(3/8) / (1/48)</gadget>
<output>18</output>
18   Answer : Option 18
<result>C</result>
P and Q can do a work in 30 days. Q and R can do the same work in 24 days and R and P in 20 days. They started the work together, but Q and R left after 10 days. How many days more will P take to finish the work?