Diameter split into three equal parts with semicircles drawn: shaded area or ratio

This type of question, asked 3 times: CDS 2 2018, CDS 1 2020, CDS 1 2024. All 3 questions below, oldest first.

Try each one first, then open its answer.

Question 1
CDS 2 2018
93 $In the figure given below, ABCD is the diameter of a circle of radius 9 cm. The lengths AB, BC and CD are equal. Semicircles are drawn on AB and BD as diameters as shown in the figure. What is the area of the shaded region ?$
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Question 2
CDS 1 2020
90 $PQRS$
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Question 3 (case study, 2 parts)
CDS 1 2024
Consider the following for the next two (02) items that follow : Let ABCD be the diameter of a circle of radius 6 cm. The lengths AB, BC and CD are equal. Semi-circles are drawn with AB and BD as diameters as shown in the figure given below.
99 $What is the ratio of the area of the shaded region to that of the non-shaded region ?$
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100 $What is the perimeter of the shaded region ?$
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Question 1