MCQ
There is a rectangular sheet of dimension $\big(2\text{m-1}\big)\times\big(2\text{n-1}\big),$ (where $m > 0, n > 0$). It has been divided into square of unit area by drawing lines perpendicular to the sides. Find number of rectangles having sides of odd unit length?
  • A
    $\big(\text{m+n+1}\big)^2$
  • B
    $\text{mn}\big(\text{m+1}\big)\big(\text{n+1}\big)$
  • C
    $4^\text{m+n-2}$
  • $\text{m}^2\text{n}^2$

Answer

Correct option: D.
$\text{m}^2\text{n}^2$
Total no. of horizontal line $= 2m$ Total no. of vertical lines $= 2n$ $($$\because$ Each line is at unit distance and hence, total no. of lines = Distance/lenght $+1).$
To form a square from three lines,we mustselect one even and one odd numbered horizontal and vertical line
$\therefore$ Ways possible of selecting such squares $=(\text{c}_{1}^\text{m})\times(\text{c}_{1}^\text{m})\times$ $(\text{c}_{1}^\text{n}\times\text{c}_{1}^\text{n})=$ $\text{c}_{1}^\text{m}\times\text{c}_{1}^\text{m}\times\text{c}_{1}^\text{n}\times\text{c}_{1}^\text{n}=$ $\text{m}^2\times\text{n}^2=\text{m}^2\text{n}^2$

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