I have what I suspect is a boringly lame question, but as my last math class was almost 20 years ago, I don't know the answer. Well, let's change that; I made a stab at it and I think I'm wrong.

Anyway, my brother emailed me - why, I haven't a clue - "What is the formula for figuring an average of two numbers, where one number represents 30% of the result?"

Jumping in feet first, I came up with;

Since the average of the two numbers is equal to their sum divided by two, then you have this;

x + y = z, where x = some number, y = some other number, and z = (x+y)/2

When you toss in the 30%, I think it comes out like this;

x + y = z, where x = some number, y = .3z and z = (x+y)/2, or y = .3((x+y)/2)

Substituting for y, you get;

x + .3z = z, or x + .3z – z = 0

Now, substituting for z, you get;

x + .3((x+y)/2) – (x+y)/2 = 0, or x + .3(x/2 + y/2) – x/2 + y/2 = 0, or x + .3x/2 + .3y/2 – x/2 + y/2 = 0

Then, this mess gets you;

x + .3/2x + .3/2y – x/2 + y/2 = 0 which can be rewritten as,

x + .15x + .15y - .5x + .5y = 0

or,

.65x + .65y = 0, or .65x = -.65y

Take out the .65 from both sides;

x = -y

Which is probably wrong and why I have always hated math.

Any help on this first grade problem?

x is the average, x = (.3x + y) / 2

2x=.3x+y

1.7x=y