A can copy 50 papers in 10 hrs, while A & B can copy 70 papers in 10 hrs. How many hours are required for B to copy 26 papers?  Choose one:  A) 11 hours  B) 12 hours  C) 13 hours  D) 14 hours  E) 18 hours
A can copy 50 papers in 10 hrs, while A &amp; B can copy 70 papers in 10 hrs.   It means B can copy 20 papers in 10 hrs.   Then time taken by B to copy 26 papers = 26*10/20= 
<gadget id="calculator">26*10/20</gadget>
<output>13</output>
13 hours   ANSWER:13 hours
<result>C</result>
A can copy 50 papers in 10 hrs, while A & B can copy 70 papers in 10 hrs. How many hours are required for B to copy 26 papers?