# Direct Variation - PowerPoint PPT Presentation

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Direct Variation. (Y = KX). Direct Variation Method “Y” varies directly as “X” means y = kx Y is a unit and X is another unit. Example: If weight varies directly as height and a person who is 73 inches tall weighs 210 lbs. then how tall is a person who weighs 180 lbs.?

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Direct Variation

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## Direct Variation

(Y = KX)

• Direct Variation Method

• “Y” varies directly as “X” means y = kx

• Y is a unit and X is another unit.

• Example: If weight varies directly as height and a person who is 73 inches tall weighs 210 lbs. then how tall is a person who weighs 180 lbs.?

• Y = weight, and X = height thus Weight = Height(K)

• 210 = 73k thus k = 210/73

• So 180 = (210/73)X; X = 180/ (210/73) = 430/7 = 62.6 inches

### Example:

• Proportion Method

• Inches/ lbs = inches / lbs

• 73 / 210 = X / 180

• 73(180) = 210x

• 12960 = 210x

• 12960 / 210 = x

• 430 / 7 = x

• X = 62.6 inches

### Example (continued)

If the volume of a polyhedron varies directly as the square root

of its surface area, when the volume is 60 cu. ft. with a

surface area 100 sq. ft. what’s the volume for a polyhedron with

a surface area of 400 sq. ft.?

• Volume = K √Surface Area

• 60 = K √100

• 60 = 10K

• 60 / 10 = K; K = 6

• So V = 6√400

• V = 6(20)

• V = 120 cu ft

### Example:

• Page 565 #’s 2 to 24 evens

• Page 572 #’s 27 to 32

• Page 579 #’s 7 to 10, 23, 24, 27 to 29