Question

Clare estimates that her brother is 4 feet tall. When they get measured at the doctor’s office, her brother’s actual height is 4 feet, 2 inches.

1.What was the error, expressed in inches?
2.What was the error, expressed as a percentage of the actual height?

Answer 1

Problem 1

The error is 2 inches since her estimate is 2 inches off the true value.

We can think of it like this

4 feet = 4*12 = 48 inches

4 feet, 2 inches = 4 ft + 2 in = 48 in + 2 in = 50 inches

So she guesses he is 48 inches, but he's really 50 inches, so 50-48 = 2 inches is her error.

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Problem 2

Divide the error (2 inches) over the actual height (50 inches) to get

2/50 = 4/100 = 4%

The percentage error is 4%

This means she is 4% off the target.

Note how 4% of 50 = 0.04*50 = 2 which was the error we found back in problem 1.