Let x be the original price of the refrigerator.
Since Alex bought the refrigerator for 2/5 of the original price, we can express that amount algebraically as:

On the other hand, he paid $400. Then, we can write down the equation:

To solve the equation, multiply both members by 5 to get rid of the denominator on the left member:

Next, divide both members by 2 to get rid of the factor of 2 that multiplies x:

Therefore, the original price of the refrigerator was $1000.