Question

19．計算：$\frac{1}{4}$×39+$\frac{3}{4}$×27．

Answer 1

分析 把$\frac{1}{4}$×39+$\frac{3}{4}$×27改寫成$\frac{1}{4}$×39+$\frac{1}{4}$×3×27，即$\frac{1}{4}$×$39+\frac{1}{4}$×81，然后再利用乘法分配律的逆運算進行計算．

解答 解：$\frac{1}{4}$×39+$\frac{3}{4}$×27
=$\frac{1}{4}$×$39+\frac{1}{4}$×3×27
=$\frac{1}{4}$×$39+\frac{1}{4}$×81
=$\frac{1}{4}$×（39+81）
=$\frac{1}{4}$×120
=30

點評 本題關鍵是要把$\frac{1}{4}$×39+$\frac{3}{4}$×27改寫成$\frac{1}{4}$×$39+\frac{1}{4}$×81來進行解答．