1) Do the following tables represent direct variation? Justify your answer.
a.
x 1 2 3 4 5
y 2 4 6 8 10
b.
x
y
1 2 3 4 5
2 4 9 12 15
2) "y varies directly as x". If y = 3 when x = 24, find y when x = 10.
3) The mass of a substance varies directly as the volume of the substance. If the mass of 2 liters of the
substance is 10 kilograms, what will be the volume of 35 kilograms of the substance?
4) The number of calories in Swiss cheese varies directly with the weight of the cheese. There are
about 200 calories in 50 grams of Swiss cheese. Willie ate 70 grams of Swiss cheese. About how
many calories did he eat?
5) If the pressure of a gas varies directly with the temperature. When the pressure is 800 psi, the
temperature is 400 . What is the temperature when the pressure is 450 psi?
6) The distance covered by a car traveling at a constant speed is directly proportional to the time
spent traveling. If the car goes 75 miles in 5 hours, how far will it go in 7 hours?
7) A salesman's commission is directly proportional to his total sales. If the commission is $100 for
$1000 in sales, find the commission for $1750 in sales.
8) The number of girls in a class varied directly as the number of boys. One class had 3 boys and 21
girls. If another class had 5 boys, how many girls were in this class?
9) The number of peach trees in the orchard is directly proportional to the number of apple trees.
When Farmer Bob planted 40 peach trees, he planted 120 apple trees. Everything was killed in
the drought and he’s starting anew. How many apple trees will he need to plant if he plants 500
peach trees?