Question

Tính bằng cách thuận tiện nhất :

a)\(\dfrac{81x49}{7x8}\) 

b)\(\dfrac{105x69}{3x35}\)  

c)\(\dfrac{77x39}{13x11}\)

Answer 1

a) \(\dfrac{81\times49}{7\times8}=\dfrac{81\times7\times7}{7\times8}=\dfrac{81\times7}{8}=\dfrac{567}{8}\)

b) \(\dfrac{105\times69}{3\times35}=\dfrac{3\times35\times69}{3\times35}=69\)

c) \(\dfrac{77\times39}{13\times11}=\dfrac{11\times7\times13\times3}{13\times11}=7\times3=21\)

Answer 2

a) \(\dfrac{81x49}{7x8}=\dfrac{81x7x7}{7x8}=\dfrac{81x7}{8}=\dfrac{567}{8}=70,875\)

b) \(\dfrac{105x69}{3x35}=\dfrac{3x35x69}{3x35}=\dfrac{69}{1}=69\)

c) \(\dfrac{77x39}{13x11}=\dfrac{11x7x3x13}{13x11}=\dfrac{7x3}{1}=\dfrac{21}{1}=21\)