Question

A large number of copies of the annual report of an organisation are to be printed. There are two printed machines. Machine A will need $10$ days to print them. Machine B will be need $15$ days. If both machines are put to use, the number of days needed for printing is

• A. $25$
• B. $6$
• C. $5$
• D. $30$

Answer 1

Answer: (B)

$6$

$letworkbe"W"thenpowerofmachineA=\left(\frac{W}{10}\right)powerofmachineB=\left(\frac{W}{10}\right)combinedpowerofboth=W\left(\right(\frac{1}{10})+(\frac{1}{15}\left)\right)=W\cdot \left(\frac{25}{150}\right)=\left(\frac{W}{6}\right)\therefore timecompletion=\left(\frac{W}{\left(\frac{W}{10}\right)}\right)=6days$