Sketch the graph of a function whose first derivative is always negative and second derivative is always positive.

Y = f(x)
y' < 0 
y'' > 0

Function must be decreasing and concave

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.