Diameter of the semicircle = 10 km.
Explanation: perimeter of semicircle = 1 2
the circumference + diameter Given: perimeter of semicircle = 25.7 k
m
Circumference of circle with radius r
= 2
π
r where 2
r
= diameter ⇒
25.7
=
22
π
r
+
2
r
⇒
25.7
=
π
r
+
2
r
=
r
(
π
+
2
) ⇒
25.7
=
r
(
3.14
+
2
)
=
r
(
5.14
) ⇒
r
=
=5m
⇒d
i
a
m
e
t
e
r
=
2
r
=
10
k
m
