Correct Answer - C
Consider the following events :
E=A speaks truth, F=B speaks truth.
We have,
P
(
E
)
=
4
5
and
P
(
F
)
=
3
4
P
Required probability
=
P
(
(
E
∩
¯¯¯
F
)
∪
(
¯¯¯
E
∩
F
)
)
=
=
P
(
E
∩
¯¯¯
F
)
+
P
(
¯¯¯
E
∩
F
)
=
=
P
(
E
)
P
(
F
)
+
P
(
¯¯¯
E
)
P
(
F
)
=
=
4
5
×
(
1
−
3
4
)
+
(
1
−
4
5
)
×
3
4
=
7
20
=