If a rectangle shaped keyboard has dimensions of 45 centimeters by 150 millimeters, what is its perimeter in centimeters?
The keyboard might look something like this with a length of 45 centimeters and a width of 150 millimeters. If we want to find the perimeter, that’s the distance all the way around this keyboard, our first step will be to take the measure of 150 millimeters and convert it to centimeters because we want to know the perimeter in centimeters. We know that there are 10 millimeters in every one centimeter. And that means we can divide the number of millimeters by 10 to get the number of centimeters. 150 divided by 10 equals 15. And so we can say that 150 millimeters equals 15 centimeters.
So we add that to our diagram. In a rectangle, we know that opposite sides have the same length which means that the top of the keyboard would also be 45 centimeters and that the other side of the keyboard would be 15 centimeters. We know the perimeter is the distance all the way around. And that means it’s the sum of all four side measures, 15 centimeters plus 45 centimeters plus 15 centimeters plus 45 centimeters. 15 plus 45 equals 60. 15 plus 45 equals 60. And so we add 60 centimeters plus 60 centimeters, and we get 120 centimeters. This keyboard would have a perimeter of 120 centimeters.