# Tutoring high school maths and sciences, unit conversions are prevalent. The math tutor offers an example of converting between common units.

Hello: hope your summer is going great. As I’ve implied over the previous few weeks, my activities have shifted from day-to-day tutoring towards maintenance and research.

One focus, particularly since early July, has been repairing my old Lawn-Boy mower. It’s been a true learning experience. A point of interest about the repair/restoration, which also connnects with math, is the notion that, according to the Lawn-Boy service manual, the engine is 3.5 horsepower. Horsepower is an imperial unit, often abbreviated to hp. The obvious question: What is 3.5 horsepower in metric?

Well, to start with, the metric unit for power is the Watt. Most metric units are lower case, but a few are upper case because they are named after people. So it is with the Watt, named after James Watt. The abbreviation for Watt is W.

From the perspective of common processes, a Watt is a very small amount of power. To make the numbers more convenient, many applications use the kilowatt, abbreviated to kW:

1kW=1000W

Now, it’s a fact that, rounded to the nearest whole number,

1hp=746W

Multiplying both sides by 3.5, we get

3.5hp=3.5(746W)=2611W

Now, we divide by 1000 to convert to kW:

2611W/1000=2.611kW

Apparently, to convert from hp to kW, we first mutliply by 746, then divide by 1000. We can combine those two operations and just multiply by 0.746, as follows:

**Example: suppose a car is rated at 220 horsepower. What is its power in kW?**

Solution:

220(0.746)=164kW, rounded to nearest whole number.

This article has evolved several topics that I’ll discuss in future posts:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.