Respuesta :
Answer:
E) is correct, 2/3
Step-by-step explanation:
The points that are 20 inches apart from P form a circle that contains Q. We can suppose that P is in the position (0,0) and Q in the position (20,0) (we can rotate and move the circle without making any effect on the probability).
A point in the circle at distance 20 of Q has the form (20 cos(Ф), 20 sen(Ф) ) for certain angle Ф between 0 and 2π. Since it is at distance 20 of Q, we have that (20-20cos(Φ))² + (0-20sen(Φ))² = 20²=400, thus
400 - 800 cos(Φ) + 400cos²(Φ) + 400sen²(Φ) = 800-800cos(Φ) = 400, so
400 = 800cos(Φ)
cos(Φ) = 1/2
By looking at a trigonimetric table, you can find that Φ is either π/3 or 2π-π/3 = 5π/3.
As a result, the angles that will give you a point R at distance from Q greater than 20 are between π/3 and 5π/3, hence , the points that are a distance greater than 20 form a chord of length 20*(5π/3-π/3) = 80π/3. Comparing this with the perimeter of the circle (20*2π = 40π), this gives us a probability of 80π/3 / 40π = 2/3 that the point R is closer to P than it is to Q.
