Quick simple question....

[WTF?]

I have this problem that I can't understand. (well, I understand half of it)

"You have some money saved from your job. You invest S of it in a savings account that pays 8% interest and the rest R in a checking account that pays 6%. You earn $84 interest in one year.

a. Write an equation relating S, R, and the total amount of interest.
b. Give three possible pairs of values for R and S.

A. 84=.8S + .6R
B. I don't understand how to rewrite it as y=mx+b.

Any help, is greatly appreciated.

 

[tkhunny]

A. 84=.8S + .6R
B. I don't understand how to rewrite it as y=mx+b.

Not quite. 84 = 0.08*S + 0.06*R
Just solve for either variable.

84 = 0.08*S + 0.06*R
0.06*R = 84 - 0.08*S
R = 84/0.06 - (0.08/0.06)*S
R = 1400 - (4/3)*S

Similarly,

84 = 0.08*S + 0.06*R
0.08*S = 84 - 0.06*R
S = 84/0.08 - (0.06/0.08)*R
S = 1050 - (3/4)*R

 

[WTF?]

ah, thank you so much. So if I'm given an equation like that, it doesn't matter which variable i solve for?

And what do they mean by possible pairs?

 

[tkhunny]

Using this one:

S = 1050 - (3/4)*R

Just pick a value for R. How about $1000?

S = 1050 - (3/4)*(1000) = 1050 - 750 = 300

There is a pair. Now, pick something else for R. Careful. There are limits to the values you can pick. Do you see why?