Troubleshooting: A=15-B, C=B+9, D=B+21

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The discussion focuses on solving a system of equations derived from the expressions A=15-B, C=B+9, and D=B+21. The equations are manipulated by multiplying each by 3 and summing them, leading to the conclusion that the average of the variables A, B, C, and D is 19.5. The calculations confirm that the total of A, B, C, and D equals 78, validating the average result. This systematic approach highlights the importance of algebraic manipulation in solving linear equations.

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View attachment 6392 I know that its well above average.

So I got A= 15-B, C=B+9 and D=B+21, but I think I made a mistake somewhere
 

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Let's denote the four numbers by $a$, $b$, $c$ and $d$. Then we have the following system.
\[
\left\{
\begin{aligned}
a+\frac13b+\frac13c+\frac13d=25\\
\frac13a+b+\frac13c+\frac13d=37\\
\frac13a+\frac13b+c+\frac13d=43\\
\frac13a+\frac13b+\frac13c+d=51\\
\end{aligned}
\right.
\]
Multiply each equation by 3 and add them. Recall that you need to find $\dfrac{a+b+c+d}{4}$.
 
6(A+B+C+D)=468

(A+B+C+D)=78

Average is 19.5?
 
You are right.
 

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