Question 1159719
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72.6%.<br>
The answer is of little use to you, unless you just want to answer the question without learning anything.<br>
So I will tell you one way you can get that answer and let you have the experience of working the problem yourself.<br>
Draw a sketch of the cross section of the tank.  It will be a circle with radius 11 with a horizontal chord 4 units above the middle of the circle.  (The depth of the water is 15ft; the radius of the tank is 11ft; the chord representing the water level is 4ft above the center).<br>
Draw the radii to the two endpoints of the chord.<br>
A radius of the tank to one end of the chord forms a right triangle, allowing you to determine the length of the chord.  (In that triangle, one leg is half of the chord; the other leg is 4ft and the hypotenuse is 11ft.)<br>
The area of the cross section of the tank that is water can be viewed as composed of two parts: (a) the area of the triangle formed by the chord and the two radii to the ends of the chord; and (b) the sector of the circle "below" those two radii.<br>
At this point you know the measures of the legs of the triangle, so you can easily determine its area.<br>
For the sector of the circle, observe that the angle above the midline of the cross section is {{{sin^(-1)(4/11)}}}.  So the angle of the sector of the circle containing water is 180 degrees plus twice that angle.<br>
The next-to-last step is to add the areas of the triangle and the sector of the circle; the last step is to convert that to a percentage by dividing that area by the area of the whole circle.<br>