Section 4.3
Solving Application
Problems Using System of
Equations
Problem solving procedure
 1. Select a variable to represent each
unknown.
 2. Write a system of equations. (# of
equations is the # of variables)
 3. Solve the system.
 4. Answer the question (include units
if applicable)
Examples, from p 231
 #12 A store has a clearance sale so that all t-
shirts sell for $12 and all shorts sell for $15.
the day the sale began, 57 clearance items sold
(t-shirts and shorts) for a total of $747. How
many t-shirts and how many shorts were sold?
 #29 A boat travels 36 miles upstream in 3
hours. Going downstream, it can travel 48
miles in the same amount of time. Find the
speed of the current and the speed of the
boat in still water.
 #32 If a plane can travel 320 miles per hour
with the wind and only 280 mph against the
wind, find the speed of the wind and the
speed of the plane in still air.
 #33 How many milliliters of a 55 HCl mixture
and a 20% HCl mixture must be combined to
get 10 milliliters of 12.5% HCl mixture?
 #34 How much of a 45% saline solution and a
30% solution must be mixed to produce 20
liters of a 39% solution?