Tính nhanh:
a) 1997 x 18 + 80 x 1997 + 3994
b) 411×713×33142\dfrac{4}{11} \times \dfrac{71}{3} \times \dfrac{33}{142}114×371×14233
= 1997 x 18 + 80 x 1997 + 1997 x 2
= 1997 x (18 + 80 + 2)
= 1997 x 100
= 199 700
b) 411×713×33142=4×71×3×1111×3×71×2=42=2\frac{4}{{11}} \times \frac{{71}}{3} \times \frac{{33}}{{142}} = \frac{{4 \times 71 \times 3 \times 11}}{{11 \times 3 \times 71 \times 2}} = \frac{4}{2} = 2114×371×14233=11×3×71×24×71×3×11=24=2