<PRE><B>Question 842047</B>
Two crews are digging an 800-meter tunnel through Marble Mountain.
 Crew A starts at the west end and digs at a rate of 9m/day.
  Five days later, Crew B starts at a rate of 10m/day.
 How many days will Crew A have been working when the tunnel is finished?
:
Let t = no. of days dug by crew A
Crew B starts 5 days later, therefore
(t-5) = no. of days dug by crew B
:
9t + 10(t-5) = 800
Find t</PRE>