Price elasticity of demand is (-1), at a given price the consumer buys 60 units of the good. How many units will the consumer buy if the price falls by 10%:

Price elasticity of demand (PED) is given as $-1$.
Initial quantity demanded ($Q_1$) is 60 units.
The price falls by $10\%$, so the percentage change in price ($\% \Delta P$) is $-10\%$.

The formula for price elasticity of demand is:

Substitute the given values into the formula:

Now, solve for the percentage change in quantity demanded ($\% \Delta Q$):

A $10\%$ increase in quantity demanded means the quantity will increase by $10\%$ of the initial quantity.
Increase in quantity = $10\%$ of 60 units

The new quantity demanded ($Q_2$) is the initial quantity plus the increase:

The consumer will buy $66 \text{ units}$.