 Lesson Objective: NCSCOS 4.01 – Students will know how to solve problems using direct variation

 The amount of a person’s paycheck varies directly with the number of hours worked. For 13 hours of work, the paycheck is $ Find the pay for 25 hours of work.  “varies directly” means:  Remember, “y” always varies directly as “x”

 The amount of a person’s varies directly with the number of For 13 hours of work, the paycheck is $ Find the pay for 25 hours of work.  If “y” varies directly as “x” than what comes before varies directly is y and what comes after it is x paycheck hours worked.

 Remember, varies directly with 3 numbers means:  In this problem it means:

 The amount of a person’s paycheck varies directly with the number of hours worked. For 13 hours of work, the paycheck is $ Find the pay for 25 hours of work.  Replace paycheck with $73.45 and hours with 13 and then 25 for hours in the second fraction

 The amount of a person’s paycheck varies directly with the number of hours worked. For 13 hours of work, the paycheck is $ Find the pay for 25 hours of work.  Replace paycheck with $73.45 and hours with 13 and then 25 for hours in the second fraction

 Cross Multiply  Solve the equation

 The number of calories in a container of milk is directly proportional to the amount of milk in the container. If there are 160 calories in an 8-ounce glass of milk, find the number of calories in a 15- ounce glass of milk.  Directly proportional means direct variation

 The number of calories in a container of milk is directly proportional to the amount of milk in the container.  Y varies directly as x, so calories is y and amount of milk is x

 The number of calories in a container of milk is directly proportional to the amount of milk in the container. If there are 160 calories in an 8-ounce glass of milk, find the number of calories in a 15- ounce glass of milk.

 Cross Multiply  Solve the equation

 Laura typed 176 words correctly in 4 minutes. Assuming a direct variation, how many words can she type in 30 minutes?  A refund you get varies directly as the number of cans you recycle. If you get a $3.75 refund for 75 cans, how much should you get for 500 cans?

 The number of miles driven varies directly with the number of gallons of gas used. Erin drove 297 miles on 9 gallons of gas. How far would she be able to drive on 14 gallons of gas?  The kinetic energy of a car varies directly with the square of the velocity of the car. A car with a velocity of 9 meters per second has 33,100 joules of kinetic energy. About how much kinetic energy does the same car have when traveling at 12 meters per second?

 The height of a kite from the ground varies directly with the cube of the wind speed. A kite flies 8 feet high when the wind speed is 10 miles per hour. What is the height of a kite when the wind speed is 25 miles per hour?