# The formula s=√18d can be used to find the speed s of a car in miles per hour when the car needs d feet to come to a complete stop after stepping on the brakes. If it took a car 25 feet to come to a complete stop after stepping on the brakes, estimate the speed of the car. Truncate the value of √18d, when d = 25, to the tenths place.

Question
Ratios, rates, proportions
The formula $$\displaystyle{s}=√{18}{d}$$ can be used to find the speed s of a car in miles per hour when the car needs d feet to come to a complete stop after stepping on the brakes. If it took a car 25 feet to come to a complete stop after stepping on the brakes, estimate the speed of the car. Truncate the value of $$\displaystyle√{18}{d}$$, when d = 25, to the tenths place.

2020-12-01
Substitute d=25 to the formula and use a calculator to evaluate: $$\displaystyle{s}=\sqrt{{18}}{\left({25}\right.}$$
$$\displaystyle{s}=\sqrt{{450}}$$
s~21,2132...
Truncated to the tenths place, we have:
s~21.2 miles per hour.

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