CONCLUSION OF RATE OF CHANGE

As you may have noticed whenever you want to calculate the "average rate of change"
for any two points, it must form the quotient:
and recalling concepts in your math course you will realize that:

is the slope of a line.
If we scale a portion of the graph and the points for which was calculated
average rate of change (slope.) between Monday and Tuesday, you can see
clearly that the average exchange ratio is the slope of the secant line
through the points (x1, y1) and (x2, y2) is:
So you can ensure the following, each to perform the calculations of reasons
average exchange, while you're calculating the slope of straight
drying (for each pair of points).