Q.
An umbrella has 8 ribs which are equally spaced (see Fig.). Assuming umbrella to be a flat circle of radius 45 cm, find the area between the two consecutive ribs of the umbrella.

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Detailed Solution
Explanation-
We know that, formula for the area of the sector of a circle
Area of the sector = θ/3600 × πr2
By observing the figure, we see that there are 8 equal ribs in an umbrella
Thus, the angle between 2 consecutive ribs = θ = 3600/8 = 450
So, here the umbrella forms flat circle
Now, the radius of the flat circle = r = 45 cm
Therefore, The area between 2 consecutive ribs of the umbrella = Area of a sector with an angle of 450 = θ3600 × πr2
=450/3600 × 22/7 × 45 × 45
= 1/8 × 22/7 × 45 ×45
= 22275/28
= 795.535 cm2

