a. (75 + 45) : 5 = ?

Cách 1: (75 + 45) : 5

= 120 : 5 = 24

Cách 2: (75 + 45) : 5

=  75 : 5 + 45 : 5

= 15 + 9

= 24

b.(88 – 32) : 8 = ?

Cách 1: (88 - 32) : 8 

 = 56 : 8 =7

Cách 2: (88 - 32) : 8  

= 88 : 8 – 32 : 8

= 11 – 4

= 7

C

c

C

Hướng dẫn giải:

a) (32 + 128) : 4 = 32 : 4 + 128 : 4 = 8 + 32 = 40 

b) 240 : (2 + 5) = 240 : 2 + 240 : 5 = 120 + 48 = 168 

32-(5-8+32)+(5-8+6)

Cách 1:

=  32 - 5 + 8 - 32 + 5 - 8 + 6

= 27 + 8 - 32 + 5 - 8 +  6

= 35 - 32 + 5 - 8 + 6

= 3 + 5 - 8 + 6

= 8 - 8 + 6

= 0 + 6 = 6

Cách 2:

32-(5-8+32)+(5-8+6)

= 32 - 5 + 8 - 32 + 5 - 8 + 6

= ( 32 - 32) + ( 5 - 5) + ( 8- 8) + 6

= 0 + 0 + 0 + 6 = 6

\(49\dfrac{8}{23}-\left(5\dfrac{7}{32}+14\dfrac{8}{23}\right)=49\dfrac{8}{23}-5\dfrac{7}{32}-14\dfrac{8}{23}=\left(49\dfrac{8}{23}-14\dfrac{8}{23}\right)-5\dfrac{7}{32}=35-5\dfrac{7}{32}=\dfrac{953}{32}\)

a, A= 1/5.6+1/6.7+1/7.8+...+1/24.25

=1/5-1/6+1/6-1/7+1/7-1/8+...+1/24-1/25

=1/5-1/25

=4/25

hok tốt k nha

a: \(A=\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{24}-\dfrac{1}{25}\)

\(=\dfrac{1}{5}-\dfrac{1}{25}=\dfrac{4}{25}\)

b: \(B=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{8}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{32}+\dfrac{1}{32}-\dfrac{1}{57}+\dfrac{1}{57}-\dfrac{1}{87}\)

\(=\dfrac{2}{15}+\dfrac{1}{8}-\dfrac{1}{87}\)

=859/3480