difficult Geometry PS

[akane]

Here is another question I came across:
Equilateral triangle ABC is inscribed in a circle with center o. the length of arc ABC is 24. What is the approximate length of the circle's diameter? there was a figure that I cannot present but imagine an equilateral triangle completely filling a circle and the arc covering most of the circle's circumference, so only bottom fraction of triangle is left out. thanks for your replies.
Choices are:
5
8
11
15
19

[Gokhra]

Here is another question I came across:
Equilateral triangle ABC is inscribed in a circle with center o. the length of arc ABC is 24. What is the approximate length of the circle's diameter? there was a figure that I cannot present but imagine an equilateral triangle completely filling a circle and the arc covering most of the circle's circumference, so only bottom fraction of triangle is left out. thanks for your replies.
Choices are:
5
8
11
15
19

Given that its an equilateral triangle, the arc ABC should cover 2/3 of the circle's circumference.

So,
(2/3)*2(pi)r = 24
r = 5.7
d = 2*5.7 = 11.4

IMO C