Lengths of Lines
Normally you use a ruler to measure and draw
lines. This next experiment is to find out how good you are at
guessing lengths. Later on we shall see if you improve with
practice.
This page is _____ long. Put your ruler away.
Guessing the Lengths
You will need Table 3 on page R2.
Figure 3 - Five lines
Figure 3 shows five lines.
| a |
Guess the length
of line 1/2
to the nearest centimetre. |
| b |
Write your guess
on the first row of Table 3 in the first column. |
| c |
Guess the lengths
of the other four lines. Write down your guesses in Table
3. |
How Accurate?
You will need Table 3.
Do not begin this section until you have
guessed the length of all five lines.
| a |
Measure each line
with your ruler. Write down the results in the second row
of the table. |
| b |
Find the error
for each line, i.e. the difference between your guess and
the true length. Write down these results in the third
row of the table. |
| c |
If your guess was
too high, put a '+' sign in the last row. If your guess
was too low, put a '-' sign in the last row. If your
guess was exactly right, leave the last row blank. |
| d |
Give your results
to your teacher. |
Your Errors
You will need Table 3.
The differences in row 3 of Table 3 are your
errors.
| a |
How many of your
five guesses were too low? |
| b |
Which guess had
the biggest error? |
| c |
Which guess had
the smallest error? |
People often make bigger errors with longer
lines.
How Good Were You on Average?
You can now calculate your mean error.
| a |
Add your five differences
together (row 3). Write down the total. This is the total
error. |
| b |
Divide this total by 5 to
get the mean error. |
| c |
Copy and complete:
My mean error shows that on average my guesses
were in error by _____ cm. |
Your teacher will discuss the class results
with you.
| 
