Name: gayle

Who is asking: Parent
Level: Middle

I don't understand the second part of this problem Here is the first part that was correct. A 35yr old has 100% blood flow. A 65yr old has 64% blood flow. Find the rate of change per yr in the percent of blood flow. (This part is correct) m=(64-100)/(35-65)= -36/30= -1.2 per year of blood flow.

Now, here is the second part I DON'T UNDERSTAND! .Let b represent the percent of blood flow and a represent a person's age. Write an equation that you could use to predict the percent of blood flow for a person of any age over 35.

Hi Gayle,

I would plot a graph showing age on the horizontal axis and percent of blood flow on the vertical axis. Put the two points that you know on the graph. (When a = 35 Years, b = 100% and when a = 65 Years, b = 64%.)

The equation that you want is the equation that describes the line joining these two points. This line has equation

b = ma + k

where m is the slope that you found in the first part of the problem, that is m = -1.2 so b = -1.2a + k.

You can find k by substituting one of the points into the equation. Substituting a = 35 and b = 100 gives

100 = -1.2(35) + k or 100 = -42 + k

Thus k = 142 and the equation is

b = -1.2a + 142
I hope this helps,

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