Math 150 – Fall 2015
Section 4A
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Section 4A – Word Problems
See video: Mixture Problems
Example 1. Suppose you have a 15% saline solution and a 30% saline solution, and
you would like to make 200 mL of a 20% saline solution. How many mL of the 15%
solution and how many mL of the 30% solution should you mix together?
See video: Time needed to do a Job
Example 2. Suppose the first painter can paint the entire house in twelve hours.
Together the two painters can paint the house three hours faster than the second painter
can by himself. How many hours would it take the second painter to paint the house
by himself?
Example 3. A boat travels at a constant speed for 2.5 hours upstream on the Mississippi River. It only takes that boat 48 min to return downstream over those same 25
miles. If the Mississippi River is flowing at a rate of 5 mph, then what would be the
boats constant speed if it was traveling in still water?
Example 4. An open box is constructed from a 4 foot by 5 foot piece of cardboard
by cutting squares of equal length from each corner and turning up the sides. Write
a function for the volume of the cardboard box in terms of the length of the cutout
square. Restrict the domain appropriately.