Video Transcript
What is the distance between the
two points shown as measured by the ruler? Is it (A) 8.6 centimeters, (B) 8.7
centimeters, or (C) 9.0 centimeters?
In this question, we are given a
figure of a ruler measuring 10 centimeters. Along the ruler there are two red
arrows marking a certain distance. We are asked to figure out what
distance it is measuring.
Before we figure out this problem,
let’s remember some information about rulers and how we can use them to measure
length. A ruler is a straight strip of
material with marks on it at various distance intervals. When measuring with a ruler, we
must set the ruler parallel to the length that we are measuring. If it is askew, we will not get an
accurate reading. Also, remember that we have to
place the ruler with the zero mark lined up with the end of the length. Now, let’s go back to the
problem.
We can see that the ruler is
measuring 10 centimeters with labels for each centimeter from zero to 10. Notice that the ruler is broken
down even more than that. Between each labeled centimeter,
there are additional marks for smaller measurements. On this ruler, there are
millimeters. And each one represents one-tenth
of a centimeter. The distance between two of the
lines with the smallest spacing is called the ruler’s resolution and is the smallest
difference in length that a ruler can measure.
Let’s take a look at the ruler and
figure out what this measurement is. We can see that the first arrow is
at the zero point on our ruler. So let’s start there. Now we move to the right and see
how many centimeters are in between the first and second arrow. The second arrow is after the mark
for eight centimeters, but before the nine centimeters mark. So we know that the measurement is
going to be between eight and nine centimeters.
Now we can take a closer look at
the marks in between eight and nine. Because each of the marks in
between measure one-tenth of a centimeter, the slightly larger mark in the middle
will be one-half of a centimeter. Let’s count how many tenths past
the eight-and-a-half-centimeter mark there are until we reach the arrow. There are two marks past this
point. This means that the arrow is
seven-tenths of a centimeter past the eight-centimeter mark. Therefore, these points are
measuring 8.7 centimeters.
Therefore, option (B), 8.7
centimeters, is the correct answer.
