Question

tính nhanh
a, 4/5 * 3/7 + 4/5 * 4/7
b, 20 * 45 + 55 * 20/35 * 1996 - 1991 * 35
c, (1 - 1/2) * (1 - 1/3) * (1 - 1/4) * (1 - 1/5)

Answer 1

a) 4/5(3/7+4/7)=4/5

câu b,c cũng dễ

Answer 2

a) 4/5 x 3/7 + 4/5 x 4/7

= 4/5 x ( 3/7 + 4/7 )

= 4/5 x 1

= 4/5

Answer 3

a) 4/5 x ( 3/7 + 4/7 )

= 4/5 x 1

= 4/5

b) 20 x 45 + 55 x 20 : 35 x 1996 - 1991 x 35

= 20 x ( 45 + 55 ) : 35 x ( 1996 - 1991 )

= 20 x 100 : 35 x 5

= 5 x 4 x 100 : 35 x 5

= 5 x 400 : 35 x 5

= \(\frac{5\cdot400}{35\cdot5}\Rightarrow=\frac{400}{35}.\)

Answer 4

a,

  4/5*3/7+ 4/5*4/7

= 4/5*(3/7+ 4/7)

=4/5*1

= 4/5

Answer 5

tính nhanh
a, 4/5 * 3/7 + 4/5 * 4/7
b, 20 * 45 + 55 * 20/35 * 1996 - 1991 * 35
c, (1 - 1/2) * (1 - 1/3) * (1 - 1/4) * (1 - 1/5)

a) 4/5 x ( 3/7 + 4/7 )

= 4/5 x 1

= 4/5

b) 20 x 45 + 55 x 20 : 35 x 1996 - 1991 x 35

= 20 x ( 45 + 55 ) : 35 x ( 1996 - 1991 )

= 20 x 100 : 35 x 5

= 5 x 4 x 100 : 35 x 5

= 5 x 400 : 35 x 5

= 5·400/35·5 ⇒=400/35 .

Answer 6

a, 4/5 * 3/7 + 4/5 * 4/7
b, 20 * 45 + 55 * 20/35 * 1996 - 1991 * 35
c, (1 - 1/2) * (1 - 1/3) * (1 - 1/4) * (1 - 1/5)

a) 4/5 x ( 3/7 + 4/7 )

= 4/5 x 1

= 4/5

b) 20 x 45 + 55 x 20 : 35 x 1996 - 1991 x 35

= 20 x ( 45 + 55 ) : 35 x ( 1996 - 1991 )

= 20 x 100 : 35 x 5

= 5 x 4 x 100 : 35 x 5

= 5 x 400 : 35 x 5

= \(\frac{40}{35}\)