For the reaction : aA+bB→ Products, the rate law is given by Rate = k[A]m[B]n. On making the concentration of A two-fold and halving that of B, the ratio of the new rate to the earlier rate of the reaction would be:
2(m−n)
(Rate)1=k[A]w[B]n;(Rate)2=k(2[A])w([B]2)n
Hence,(rate)2(rate)1=2m×(12)n=2m−n