若1/a+1/b=75%,1/a+1/b+1/c=5/6,则c=_.

问题描述:

1
a
+
1
b
=75%,
1
a
+
1
b
+
1
c
=
5
6
,则c=______.

因为

1
a
+
1
b
=75%,
1
a
+
1
b
+
1
c
=
5
6

所以
1
c
=
5
6
-75%=
5
6
-
3
4
=
1
12

所以c=12.
故答案为:12.