A and B can do a piece of work in 7 days, B and C in 8 days, C and A in 9 days. How long will C take to do it? Choose one:
A) 14.1 days B) 18.8 days C) 21.4 days D) 24.3 days E) 26.5 days
2c = 1/8 + 1/9 – 1/7 = 47/504   c = 47/1008 =&gt; 1008/47 = 21.4 days   The answer is 21.4 days.
<result>C</result>
A and B can do a piece of work in 7 days, B and C in 8 days, C and A in 9 days. How long will C take to do it?