Answer: 74.8%

This answer is approximate.
The value is rounded to the nearest tenth of a percent.

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Explanation:

Let,
X = area of the larger circle
Y = area of the smaller circle
Z = area of the shaded region = X - Y

The goal is to compute the ratio Z/X to get the answer we want

Let's find area of the larger circle
Area of circle = pi*(radius)^2
A = pi*r^2
X = pi*8.01^2
X = 64.1601pi
This is the exact area in terms of pi

Now repeat for the smaller circle
A = pi*r^2
Y = pi*4.02^2
Y = 16.1604pi

Subtract those results to find the value of Z
Z = X-Y
Z = 64.1601pi-16.1604pi
Z = 47.9997pi
This is the exact area of the red donut region

Divide Z over X to get the probability of landing in the red region
Z/X = (47.9997pi)/(64.1601pi)
Z/X = (47.9997)/(64.1601) <--- note how the pi terms cancel
Z/X = 0.74812 which is approximate

Convert to a percent
Move the decimal point 2 spots to the right
0.74812 ---> 74.812%

Then round this to one decimal place
74.812% ---> 74.8%

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3 years ago