Help me with some Math!

A roller-blader can skate at a speed of 21 miles per hour. If the radius of the wheels are 1.2 inches, how many revolutions per minute are the wheels turning?

Question

Help me with some Math!

A roller-blader can skate at a speed of 21 miles per hour. If the radius of the wheels are 1.2 inches, how many revolutions per minute are the wheels turning?

mrnood · Answer

this is mainly about converting units.

First - work out the circumference of the wheel in INCHES  (= 2*pi*r)

Then work out how many miles per MINUTE the speed is

Then work out howm many INCHES per minute that is

divide that by the circumference to get the revolutions per minute (that is your answer)

steve816 · Answer

I don't understand :( can you show me an example?

badhi · Answer

which of part of the MrNoods answer dont you understand? :/

steve816 · Answer

I know that the circumference is 2.4 pi but I can't figure out the rate :/

mrnood · Answer

there are 60 minutes in 1 hour

21 miles per hour = ?? miles per minute?

triciaal · Answer

other approach
21 miles per hour  60min = 1 hr  so 21 miles per 60 min
to get per minute divide by 60
(21/60) miles per 1 min

mrnood · Answer

there are 1760 yards in 1 mile
there are 3 feet in 1 yard
there are 12 inches in 1 foot

HOW many inches are there in 1 mile?

steve816 · Answer

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