Let the company sell 100 units for $100 each. Total revenue = 10000
Now price drops by 50% ($50) but revenue remains unchanged .

X*50 = 10000
X = 200 - 100% increase.

You are asked %increase(units) / % decrease(cost) = 100/50 = 2

The question states that the total revenue remains unchanged after the discount. As, you know that the total revenue is a product of number of products and the price of the product, the total revenue is equal to price * number of units sold.

Let the initial price of the product be I, Then the discounted price of the product is 0.5*I
Let the number of the units sold before discount be U, and the number of units sold after discount be u

Total revenue = I*U = 0.5*I*u
Implies, u = 2U, i.e. a 100% increase in the number of units sold.

Ratio of the percent increase in the units sold to the percent decrease of the original price for this product = 100%/50% = 2.0

Answer D

let the number of initial units = 10
Initial cost = 10

Total amount = 10*10 = 100

Final cost = 5
So, the number of units must be 20 to make the product =100

i.e. 100% increase

Ration - [spoiler]100/50 = 2[/spoiler]