The scatter plot below shows the number of prom tickets sold over a period of 7 days. the line of best fit drawn on the plot shown is used to predict the number of tickets sold on a certain day. use the two points shown on the line of best fit to calculate its slope to the nearest tenth.

The slope of the line to the nearest tenth is:

                              4.2

Clearly after looking at the scatter plot we observe that the line of best fit passes through the points:

(1,30) and (7,55)

We know that the slope of any line passing through two points (a,b) and (c,d) is calculated by the formula:

Here we have:

 (a,b)=(1,30)   and   (c,d)=(7,55)

Hence, the slope is:

Hence, the slope of the line of best fit is:

                      4.2

the answer is 40.

proof: