P and Q can complete a work in 20 days and 12 days respectively. P alone started the work and Q joined him after 4 days till the completion of the work. How long did the work last?
Select:	A) 5 days	B) 10 days	C) 14 days	D) 22 days	E) 26 days
Explanation :   Work done by P in 1 day = 1/20   Work done by Q in 1 day = 1/12   Work done by P in 4 days = 4 × (1/20) = 1/5   Remaining work = 1 – 1/5 = 4/5   Work done by P and Q in 1 day = 1/20 + 1/12 = 8/60 = 2/15   Number of days P and Q take to complete the remaining work = (4/5) / (2/15)= 
<gadget id="calculator">(4/5) / (2/15)</gadget>
<output>6</output>
6   Total days= 4 + 6= 
<gadget id="calculator">4 + 6</gadget>
<output>10</output>
10   Answer : Option 10 days
<result>B</result>
P and Q can complete a work in 20 days and 12 days respectively. P alone started the work and Q joined him after 4 days till the completion of the work. How long did the work last?