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UPSC CDS 2 2018 Math Paper
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© examsnet.com
Question : 98
Total: 100
In the figure given below, the diameter of bigger semicircle is 108 cm. What is the area of the shaded region ?
[2018 CDS-II]
201 π
c
m
2
186.3 π
c
m
2
.5 π
c
m
2
769.5 π
c
m
2
Validate
Solution:
Let the radius of smaller circle be r.
(
54
−
r
)
2
+
27
2
=
(
27
+
r
)
2
⇒
2916
+
r
2
−
108
r
+
729
=
729
+
r
2
+
54
r
⇒
2916
=
162
r
⇒
r
=
18
c
m
Area of unshaded region
=
π
(
18
)
2
+
2
×
1
2
π
(
27
)
2
=
1053
π
Area of largest semicircle
=
1
2
×
π
(
54
)
2
=
1
2
×
2916
π
=
1458
π
Area of shaded region
=
1458
π
−
1053
π
=
405
π
c
m
2
© examsnet.com
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