### Home > CC1 > Chapter 3 > Lesson 3.1.1 > Problem 3-20

3-20.

Draw the

^{rd}and^{th}figures.Can you see a pattern in the completed figures? Use this pattern to complete figures 3 and 5.

How many dots will there be in the

^{th}figure?The number of dots can be found by multiplying the figure number by

and then adding . Do this with the figure number equal to . dots Is there a figure that will have exactly

dots? If so, which figure is it?

Do the same process as above, but in reverse. Subtract

and then divide by . If you get a whole number, that is the figure number.

Use the eTool below to create the patterns for Fig. 3 and Fig. 5.

Click the link at right for the full version of the eTool: *3-20 HW eTool*