Answer:
To calculate the percentage increase in price, we can use the following formula:
Percentage Increase = (New Value - Old Value) / Old Value * 100%
In this case, the old value is $400, and the new value is $500. Let's calculate the percentage increase:
Percentage Increase = (500 - 400) / 400 * 100%
= 100 / 400 * 100%
= 25%
Therefore, the price of the smartphone increased by 25%.