a,2,5*4*9,3=10*9,3=93

b,0,5*2*3,8=10*3,8=38

c,7,61*10=76,1

d,6,7*(5,3+4,7)=6,7*10=67

A) 93

B)3,8

C)7.61

D)67

a,2,5*4*9,3=10*9,3=93

b,0,5*2*3,8=10*3,8=38

c,7,61*10=76,1

d,6,7*(5,3+4,7)=6,7*10=67

 b, 4 x 0,75 x 2,5

= (4 x 2,5) x 0,75

= 10 x 0,75

= 7,5

A. 5 x 25,7-25,7+25,7 x 6

=25,7x(5+1-6)

=25,7x0

=0

B. 4 x 0,75 x 2,5

=(4 x 2,5)x0,75

=10 x 0,75

=7,5

Lời giải:
$2,5\times 20,23\times 8\times 5=2,5\times 20,23\times 4\times 2\times 5$

$=(2,5\times 4)\times 20,23\times (2\times 5)$

$=10\times 20,23\times 10=20,23\times 100=2023$

=(0,2+24)x5

=14

\(\dfrac{2}{7}\times\dfrac{1}{5}+0,2\times\dfrac{4}{7}\)

\(=\dfrac{2}{7}\times\dfrac{1}{5}+\dfrac{1}{5}\times\dfrac{4}{7}\)

\(=\dfrac{1}{5}\times\left(\dfrac{2}{7}+\dfrac{4}{7}\right)\)

\(=\dfrac{1}{5}\times\dfrac{6}{7}\)

\(=\dfrac{6}{35}\)

2,5 × 5 × 0,2 = 2,5 × 1

= 2,5

2,5 x 7,8 x 4 = (2,5 x 4) x 7,8 = 10 x 7,8 = 78

… = (2,5 x 4) x 7,8

= 10 x 7,8

= 78 

8,36 x 5 x 0,2 = 8,36 x (5 x 0,2) = 8,36 x 1 = 8,36