Solution: Let the purchase price be X yuan.

( 1+50%)x*0.9-50=x+370

1.5*0.9x-x=370+50

0.35x=420

x= 1200

2. Numerical solution

(370+50)/( 1.5*0.9- 1)

=420/0.35

= 1200 (yuan)

A: The purchase price of this commodity is X yuan.