if a ferris well take 45 seconds to make a complete rotation how many rotations will is complete in 3 hours

## if a ferris well take 45 seconds to make a complete rotation how many rotations will is complete in 3 hours

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# 2 Answers

Hi Jerry;

[(1 rotation)/(45 seconds)][(60 seconds)/(1 minute)][(60 minutes)/(1 hour)]=(x rotations)/(3 hours)

Let's note that the unit of seconds is in the numerator and denominator. It cancels.

Let's note that the unit of minutes is in the denominator and numerator. It cancels.

[(1 rotation)/(45 seconds)][(60
seconds)/(1
minute)][(60 minutes)/(1 hour)]=(x rotations)/(3 hours)

[(1 rotation)/(45)][(60)/(1)][(60)/(1 hour)]=(x rotations)/(3 hours)

The unit of rotations/hour is on both sides of the equation. It cancels...

[(1 rotation)/(45)][(60)/(1)][(60)/(1
hour)]=(x
rotations)/(3 hours)

[(1)/(45)][(60)/(1)][(60)/(1)]=(x)/(3)

(1/45)(60)(60)=x/3

80=x/3

Cross-multiply...

240=x

240 rotations will occur in 3 hours.

This is a great example of a unit conversion problem. The key is to have the final unit be the answer unit, in this case, rotations.

1 rotation/45 seconds * 60 seconds / minute * 60 minutes / hour * 3 hours = 3600*3/45 = 240 rotations.

Checking our work: 240 rotations * 45 seconds =10800 seconds or 180 minutes or 3 hours.