the propeller spins

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 am; Location: India; Thanked: 267 times; Followed by:80 members; GMAT Score:760

the propeller spins

by sanju09 » Thu Feb 26, 2009 6:20 am

The end of a blade on an airplane propeller is 10 feet from the center. If the propeller spins at the rate of 1,320 revolutions per second, how many miles will the tip of the blade travel in one minute? (1 mile = 5,280 feet)

A. 200 pi
B. 240 pi
C. 300 pi
D. 480 pi
E. 1,200 pi

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Source: Beat The GMAT — Problem Solving | Thu Feb 26, 2009 6:20 am

satish.nagdev: Master | Next Rank: 500 Posts; Posts: 130; Joined: Sat Dec 29, 2007 5:35 am; Location: SGP; Thanked: 5 times

C?

by satish.nagdev » Thu Feb 26, 2009 9:54 am

I think its C

1320*60 ==> per minute revolutions
circumference of circle with radius 10ft = distance of one revolutions
2piR = 2*10*pi =20pi

so 20*pi*1320*60/5230 = 300

if i'm wrong correct me

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hk: MBA Student; Posts: 532; Joined: Wed Jan 28, 2009 1:39 pm; Location: Barcelona; Thanked: 33 times; Followed by:9 members; GMAT Score:640

by hk » Thu Feb 26, 2009 11:13 am

10 feet = 10/5280 miles = 1/528

Perimeter of the circular path = 2*pi*1/528
So in one sec, distance travelled by the edge of the blades =
2*pi*1/528*1320

So in 60 secs (one min) => 2*pi*1/528*1320*60 = 300pi

So answer = C

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marcusking: Master | Next Rank: 500 Posts; Posts: 106; Joined: Wed Feb 04, 2009 6:09 am; Location: Louisville, KY; Thanked: 8 times

Re: the propeller spins

by marcusking » Thu Feb 26, 2009 11:14 am

sanju09 wrote:The end of a blade on an airplane propeller is 10 feet from the center. If the propeller spins at the rate of 1,320 revolutions per second, how many miles will the tip of the blade travel in one minute? (1 mile = 5,280 feet)

A. 200 pi
B. 240 pi
C. 300 pi
D. 480 pi
E. 1,200 pi

C. 300 pi

Circumference of circle created by spinning propeller is 20pi.
20pi * 1,320 revolutions = 25400 pi

5,280/60 = 88 (reduce to feet per minute)
25400pi / 88 = 300 pi