SOLUTION: Mario leaves the office and drives downtown at 48 mph. Danica leaves at the same time driving in the same direction at 42 mph. If Mario leaves office at 5:00 pm, at what time they

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Question 1148943: Mario leaves the office and drives downtown at 48 mph. Danica leaves at the same time driving in the same direction at 42 mph. If Mario leaves office at 5:00 pm, at what time they will be 15 miles apart?
Jimmy's Plane leaves at 9:00 am at 40 mph. An hour later, Sally's plane leaves the same airport travelling in the same direction at 60 mph. At what time will Sally's plane catch up to Jimmy's ?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +t+ = the amount of time after they both
leave until they are +15+ miles apart
Let +d+ = the distance in miles that Danica
( the slower one ) has traveled when Mario has traveled
+d+%2B+15+ miles
---------------------------------
Danica's equation:
(1) +d+=+42t+
Mario's equation:
(2) +d+%2B+15+=+48t+
------------------------------
(2) +d+=+48t+-+15+
+42t+=+48t+-+15+
+6t+=+15+
+t+=+2.5+
5 PM + 2.5 hrs = 7:30 PM
when they are 15 mi apart
-------------------------------
check answer:
(1) +d+=+42t+
(1) +d+=+42%2A2.5+
(1) +d+=+105+ mi
and
(2) +d+%2B+15+=+48t+
(2) +d+=+48t+-+15+
(2) +d+=+48%2A2.5+-+15+
(2) +d+=+120+-+15+
(2) +d+=+105+ mi
OK
===========================================
Let +t+ = time in hrs for Sally's plane to
catch up with Jim's
Let +d+ = distance in miles Sally's plane
travels to catch up with Jim's
Let +d%5B1%5D+=+40%2A1+. This is Jimmy's head start in miles.
-----------------------------------------------
Sally's equation:
(1) +d+=+60t+
Jimmy's equation:
(2) +d+-+d%5B1%5D+=+40t+
--------------------------------
(2) +d+-+40+=+40t+
(2) +d+=+40t+%2B+40+
---------------------------------
+60t+=+40t+%2B+40+
+20t+=+40+
+t+=+2+
Sally catches up at 9 AM + 1 + 2 = 12 noon
----------------------------------------------
check answer:
(1) +d+=+60t+
(1) +d+=+60%2A2+
(1) +d+=+120+ mi
and
(2) +d+-+d%5B1%5D+=+40t+
(2) +d+-+40+=+40%2A2+
(2) +d+=+80+%2B+40+
(2) +d+=+120+ mi
OK