14.35.5+10.25.7+20.7 tính nhanh

Đáp án:

\(\begin{array}{l}14.35.5 + 10.25.7 + 20.7\\ = 2.7.35.5 + 250.\left( {4 + 3} \right) + 140\\ = 10.35.7 + 250.4 + 250.3 + 140\\ = 10.245 + 1000 + 750 + 140\\ = 2450 + 1000 + 890\\ = 2000 + 400 + 50 + 1000 + 800 + 50 + 40\\ = 3000 + 1300 + 40\\ = 4340\end{array}\)

Giải thích các bước giải:

$$\eqalign{ & 14.35.5 + 10.25.7 + 20.7 \cr & = 2.7.7.5.5 + 10.5.5.7 + 10.2.7 \cr & = 10.7.7.5 + 10.5.5.7 + 10.2.7 \cr & = 10.7\left( {7.5 + 5.5 + 2} \right) \cr & = 10.7.62 \cr & = 10.7\left( {60 + 2} \right) \cr & = 10.7.60 + 10.7.2 \cr & = 4200 + 140 \cr & = 4340 \cr} $$