Question

Tính bằng cách thuận tiện nhất :

\(\dfrac{42\times45}{5\times7}\) 

\(\dfrac{54\times56}{7\times9}\)

 

Answer 1

\(\dfrac{42x45}{5x7}=\dfrac{7x6x5x9}{5x7}=\dfrac{54}{1}=54\)

\(\dfrac{54x56}{7x9}=\dfrac{6x9x7x8}{7x9}=\dfrac{48}{1}=48\)

Answer 2

`(42 xx45)/(5xx7) =( 6xx7xx9xx5)/(5xx7) = 6 xx9 = 54`

`(54xx56)/(7xx9) = (9xx6xx7xx8)/(7xx9) = 6xx8 = 48`

Answer 3

đúng

 

Answer 4

\(\dfrac{42\times45}{5\times7}\) \(=\) \(\dfrac{6\times7\times5\times9}{5\times7}\) \(=\) \(6\) \(\times\) \(9\) \(=\) \(54\) 

\(\dfrac{54\times56}{7\times9}\) \(=\) \(\dfrac{6\times9\times7\times8}{7\times9}\) \(=\) \(6\) \(\times\) \(8\) \(=\) \(48\)