A tire measures 20 in. in diameter. How many revolutions will the tire have completed when its traved 100 yards?

Question

Please explain how to solve in terms a 7th grader will understand.

Answer 1

We are essentially making the circle "O" into a line "_" and repeating that line over and over again into we reach 100 yards. So we need to find the perimeter--the line around, as it were--of that circle.

 

P_circle = 2πr, or πd (2*radius is the same as the diameter)

d = 20 inches

π ≈ 3.14

P_circle = 20 in * 3.14 = 62.8 inches

 

Now we need to convert yards into inches:

^{3 ft} / _yd & ^{12 in} / _ft

That gives us:

100 yd * ^{3 ft}/_yd * ^{12 in}/_ft

3600 inches

 

Now we divide:

3600 inches / 62.8 inches = 57.324 rotations