There are a lot of houses such that the numbers of their doorplates are odd numbers and the first number of the doorplates is 685, the last number of the doorplates is 705. How many houses are there?  Choose the correct choice.
A) 12
B) 11
C) 13
D) 9
E) 10
So it starts from 685 and goes like 687, 689,...... 705. and both first and last number are inclusive. Since every other number is odd, it's just 1/2 of the numbers and since it starts with an odd and ends with an odd inclusive add one to the result.   i.e., ([705-685][/2]+1 = 11   Ans 11
<result>B</result>
There are a lot of houses such that the numbers of their doorplates are odd numbers and the first number of the doorplates is 685, the last number of the doorplates is 705. How many houses are there?