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

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The discussion revolves around solving a system of equations involving four variables: A, B, C, and D. The equations are derived from the relationships A=15-B, C=B+9, and D=B+21. After multiplying the equations by 3 and summing them, the total for A+B+C+D is found to be 78. Consequently, the average of the four numbers is calculated to be 19.5, confirming that the initial assumption of being above average is correct. The calculations validate the relationships between the variables and their average.
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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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