In the figure,above a equilateral triagle

[dilipgmat]

Hi Guys ,

Fnd this Q on GMAT prep
http://xs.to/xs.php?h=xs942&d=09331&f=sector216.jpg


Kindly refer to this image.

My approach was that Sector ABC would comprise of arc AB and AC. Which subtend angle BAC and angle ACB. They are 60 degree each.

there fore (60/360)*2*pi*r + (60/360)*2*pi*r=24

We get appr 15 as the answer. Which is wrong??
Guys m i missing something here. Do we need to consider the angle subtended at the center also !!!
Thanks In Advance

EDITED TO ADD: I deleted your post below as instructors answer questions from oldest to newest. Don't try to bump your post to the top or it will take longer to get it answered! - Brie Truesdell, studentservices@manhattangmat.com

[RonPurewal]

hi -

you're using the right formula for the wrong thing.

when you use (degrees/360) times circumference, that formula applies to the degrees of arc, not the degrees of any angle.

so those 60's should be 120's. the rest of your approach would then be valid, and would yield the correct answer (11).

by the way, how'd you get 15? if you solve your equation, you should come up with an approximate diameter of something like 22-23 (remember that this is incorrect).

the easier way to solve this problem is to realize that the given arc length of 24 makes up exactly 2/3 of the circumference, so that the whole circumference is 36.
since circumference is pi times diameter, the diameter is thus 36 divided by pi, and is thus about 11.
(remember that pi is just a bit greater than 3, so 36/pi is just a bit less than 36/3 = 12.)

[tigerwoods]

we cannot see the picture in the question rendering this post useless

[Ben Ku]

true ...