Question: there is a page ($9\times 9$) how many different rectangles can you draw with odd area?

rectangles are different if they are different on size and place.

for example if a rectangle is $15$ squares, its area is odd. 
if a rectangle is $12$ squares, its area is even.

I have no idea how to approach this question so I can't give my answer.

Thanks!

Answer: 
If the area has to be odd, the length and breadth both have to be odd. Hence, we count the number of rectangles by first choosing a row and a column ($10 \cdot 10$ ways to do this), and then choosing another row and column which are at an odd distance from the chosen one ($5 \cdot 5$ ways to do this). But we have counted each rectangle four times -- by the first row/column and then again by the second row/column -- so we divide by 4 to get our final answer: $1/4 \cdot 10 \cdot 10 \cdot 5 \cdot 5 = 625$.
the number of squares with equal dimensions is $81$. so if number of squares is odd then the rectangle has an odd area. the total rectangles are given by ${10 \choose 2}.{10 \choose 2}=2025$ . you have rectangles now you just need to select two lines which are odd distances apart from each other . and its done. hope its clear.