Hướng dẫn giải:

a. 88 + 75 + 12 = (88 + 12) + 75 = 100 + 75 = 175

b. 146 + 55 + 54 = (146 + 54) + 55 = 200 + 55 = 255.

 o0                                                   rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr                           ẻu

=(12+88) +(34+46)*2+(55+65)=100+2*80+120=100+160+120=380

kết quả là 380

12 + 34 + 88 + 46 + 55 + 34 + 65 + 46

= (12 + 88) + (34 + 46) + ( 55 + 65) + ( 34 + 46)
= 100 + 80 + 120 + 80

= 380

\(\dfrac{7}{5}\times\dfrac{11}{24}\times\dfrac{5}{7}\times\dfrac{24}{55}\\ =\left(\dfrac{7}{5}\times\dfrac{5}{7}\right)\times\left(\dfrac{11}{24}\times\dfrac{24}{55}\right)\\ =1\times\dfrac{1}{5}\\ =\dfrac{1}{5}\)

\(\dfrac{7x11x5x24}{5x24x7x55}\)=\(\dfrac{11}{55}\)=\(\dfrac{1}{5}\)

= (7/5 x 5/7) x (11/24 x 24/55)

= 1 x 1/5

= 1/5

[88 :  8]   x 12 = 132

( 88 x 12 ) : 8 = ( 88 : 8 ) x 12

                      = 11 x 12

                      = 132

Tính nhanh 28,2 x( 12 + 88)=  28,2 x 100

= (88 : 8) x 12

= 11 x 12 

= 132

nhầmd

( 88 x 12 ) : 8

=( 88 : 8 ) x 12

= 11 x 12

= 132

( 88 x 12 ) : 8

= ( 88 : 8 ) x  12

= 10 x 12

= 120

HT

= 11(1+2+3+4+5+6+7+8+9) = 11 * 9(9+1) = 11*9*10 = 990

11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99

= (11 + 99) + (22 + 88) + (33 + 77) + (44 + 66) + 55

= 110 + 110 + 110 + 110 + 55

= 110 x 4 + 55

= 440 + 55

= 495 

11+22+33+44+55+66+77+88+99

=(11+99)+(22+88)+(33+77)+(44+66)+55

=110+110+110+110+55

=110x4+55

=440+55

=495

a)     (48 x 55) : 8

= (48:8)x55

= 6x55

= 330

b)    (164 x 42) : 7

= 164x(42:7)

= 164x6

= 984

c)     (135 x 25) : 5

= 135x(25:5)

= 135x5

= 675

d)    (147 x 12) : 6

= 147x(12:6)

= 147x2

= 294

(Nếu đúng thì cho mk tick nhé)

11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99

= (11 + 88) + (22 + 77) + (33 + 66) + (44 + 55)  + 99

 =      99       +       99      +      99        +      99       + 99

= 99 x 5

= 495