Discussion

On solving algebraic expression 2(x - 2y) +4(2y + 3z) -3(x + 4y - 5z), answer will be

Answer: B

Expand each bracket, then collect.

\[ 2(x - 2y) = 2x - 4y \]

\[ 4(2y + 3z) = 8y + 12z \]

\[ -3(x + 4y - 5z) = -3x - 12y + 15z \]

\[ x: \ 2 - 3 = -1; \quad y: \ -4 + 8 - 12 = -8; \quad z: \ 12 + 15 = 27 \]

\[ \therefore\ -x - 8y + 27z \]

The \( -3 \) turns \( -5z \) into \( +15z \), which is what makes the \( z \) coefficient large and positive.

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