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