ACT Preparation / Unit 11 ACT 1030 short lesson, about 20 seconds
Inverse and Joint Variation
Captions available
The idea
y varies inversely with x when y = k/x: doubling x halves y. y varies jointly with x and z when y = kxz.
In practice
Travel time varies inversely with speed: 3 hours at 40 miles per hour gives k = 120, so 60 miles per hour takes 2 hours.
Where people slip
Inverse does not mean subtracting: it means the product xy stays constant.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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