Let $a_{n}\;$ be $\;n^{th}$ term of AP. If $\;\displaystyle\sum_{r=1}^{50}\;a_{2r}=p\;and \;\displaystyle\sum_{r=1}^{50}\;a_{2r-1}=q\;$ the common difference is :

Question

$(a)\;p-q\qquad(b)\;q-p\qquad(c)\;\frac{p-q}{100}\qquad(d)\;\frac{p-q}{50}$