Solution — 2025 Question 1 Simultaneous Linear Equations

$\begin{matrix} 2 r + 0.4 g & = 136 & (1) \end{matrix}$

[working for first equation]

$\begin{matrix} 0.75 b & = 0.6 g \\ 0.6 g - 0.75 b & = 0 & (2) \end{matrix}$

[working for second equation]

$\begin{matrix} r + g + b & = 204 & (3) \end{matrix}$

[working for third equation]

Solving equations (1), (2) and (3) with a GC,

$\begin{matrix} r = 51, g = 85, b = 68 \end{matrix}$

[solution to the system of equations]

$\begin{matrix} Number of red bricks & = 51 ∎ \end{matrix}$

[required answer for number of red bricks]