# Determining a Missing Data Value in Weighted Average

When dealing with weighted averages, how do you solve for X?

$$\frac{( 84X) + (40*16)}{100} = 10.5 .$$

• This is just a linear equation in $X$. You remember your algebra and perform the same operations on each side of the equation toward the goal of isolating $X = ...$. I edited your question to format the mathematics - that might help you. If you're really stuck and need to do this just once, try guess-and-check. When you're done, answer your own question (that's allowed on this site). – Ethan Bolker Dec 26 '16 at 19:34
• @EthanBolker Sadly I've forgotten far too much of my algebra to figure it out that way, and Google hasn't been much help in that regard ;-) – Chaya Cooper Dec 26 '16 at 20:10

1. Remove the fraction by multiplying both sides by $100$.
2. Isolate the $X$ term by subtracting the $(40*16)$ from both sides.
3. Remove the coefficient of $X$ by dividing both sides by $84$.
• @ChayaCooper And as written, that should be the correct answer. I'm not sure how one would be getting $5$ as an answer. – Simply Beautiful Art Jan 2 '17 at 19:26