a) 35 x 2 x 9 x 5

= (35 x 9) x (2 x 5)

= (35 x 10 - 35) x 10

= (350 - 35) x 10

= 315 x 10 = 3150

b) 24 x 71 + 71 x 75 + 71

= 71 x (24+75+1)

=71 x 100

= 7100

giúpppppppppppppppppppppppppppppppppppp

\(\dfrac{2}{7\times9}+\dfrac{2}{9\times11}+\dfrac{2}{11\times13}+...+\dfrac{2}{75\times77}\)
\(=\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{13}+...+\dfrac{1}{75}-\dfrac{1}{77}\)
\(=\dfrac{1}{7}-\dfrac{1}{77}\)
\(=\dfrac{11}{77}-\dfrac{1}{77}\)
\(=\dfrac{10}{77}\)

\(\dfrac{2}{7x9}+\dfrac{2}{9x11}+\dfrac{2}{11x13}+...+\dfrac{2}{75x77}\)

= \(\dfrac{9-7}{7x9}+\dfrac{11-9}{9x11}+\dfrac{13-11}{11x13}+...+\dfrac{77-75}{75x77}\)

= \(\dfrac{9}{7x9}-\dfrac{7}{7x9}+\dfrac{11}{9x11}-\dfrac{9}{9x11}+\dfrac{13}{11x13}-\dfrac{11}{11x13}+...+\dfrac{77}{75x77}-\dfrac{75}{75x77}\)

=\(\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{13}+...+\dfrac{1}{75}-\dfrac{1}{77}\)

=\(\dfrac{1}{7}-\dfrac{1}{77}=\dfrac{11}{77}-\dfrac{1}{77}=\dfrac{10}{77}\)

a: 9/11=1-2/11

11/13=1-2/13

mà -2/11<-2/13

nên 9/11<11/13

b: 19/15=1+4/15

15/11=1+4/11

mà 4/15<4/11

nên 19/15<15/11

Hướng dẫn giải:

a) 280 x 71 : 14 = (280 : 14) x 71 = 20 x 71 = 1420

b) 125 x 88 : 11 = 125 x (88 : 11) = 125 x 8 = 1000

\(\dfrac{5}{13}\times\dfrac{7}{11}+\dfrac{5}{13}\times\dfrac{2}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{5}{13}\times\left(\dfrac{7}{11}+\dfrac{2}{11}\right)+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{5}{13}\times\dfrac{9}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{9}{11}\times\left(\dfrac{5}{13}+\dfrac{8}{13}\right)\)

\(=\dfrac{9}{11}\times1\)

\(=\dfrac{9}{11}\)

a) \(20,23\times21+20,23\times80-20,23\)

\(=20,23\times\left(21+80-1\right)\)

\(=20,23\times100\)

\(=2023\)

\(\dfrac{5}{13}\) \(\times\) \(\dfrac{7}{11}\) + \(\dfrac{5}{13}\) \(\times\) \(\dfrac{2}{11}\) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\left(\dfrac{5}{13}\times\dfrac{7}{11}+\dfrac{5}{13}\times\dfrac{2}{11}\right)\)+ \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{5}{13}\)\(\times\) (\(\dfrac{7}{11}\) + \(\dfrac{2}{11}\)) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{5}{13}\) \(\times\) \(\dfrac{9}{11}\) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{9}{11}\) \(\times\)( \(\dfrac{5}{13}\) +\(\dfrac{8}{13}\))

= \(\dfrac{9}{11}\) \(\times\) 1

= \(\dfrac{9}{11}\)

a, 325

b, 700

c, 386

d, 488

k mk nnha

325  

700

386

488

giải ra đi

\(\frac{9}{4}x\frac{13}{10}-\frac{3}{4}x\frac{11}{10}+\frac{3}{4}:\frac{10}{72}\)

\(=\frac{39}{4}x\frac{3}{10}-\frac{11}{4}x\frac{3}{10}+\frac{72}{4}x\frac{3}{10}\)

\(=\frac{3}{10}x\left(\frac{39}{4}-\frac{11}{4}+\frac{72}{4}\right)\)

\(=\frac{3}{10}x25\)

\(=\frac{15}{2}\)

= 3x3/4x13/10-3/4x11/10+3/4x72/10

= 3/4x(3x13/10-11/10+72/10)

= 3/4x10

=30/4

=15/2

mih nha

bạn tách 9/4 × 13/10 làm sao

(25x36):9+450-75-25

= 900 : 9 + 450 - 75 -25

= 100 + ( 450 - 75-25)

= 100 + 350

= 450

450

=450

a)425-84-16=425-(84+16)=425-100=325.

b)821-73-27-21=(821-21)-(73+27)=800-100=700.

c)475-(75-36)=(475-75)+36=400+36=436.

d)573-(73-24)=(573-73)+24=500+24=524.

k nha có j kb vs mk

a) 425 - 84  - 16

= 425 - (84 + 16)

= 425 - 100

= 325

b) 821 - 73 - 27 - 21

= (821 - 21) - (73 + 27)

= 800 - 100

= 700

c) 475 - (75 - 36)

= 475 - 75 + 36

= 400 + 36

= 436

d) 573 - (73 - 24)

= 573 - 73 + 24

= 500 + 24

= 524

a) 425 - 84 - 16 = 425 - ( 84 + 16 ) = 425 - 100 = 325

b) 821 - 73 - 27 - 21 = ( 821 - 21 ) - ( 73 + 27 ) = 800 - 100 = 700

c) 475 - ( 75 - 36 ) = 475 - 75 + 36 = ( 475 - 75) + 36 = 400 + 36 = 436

d) 573 - ( 73 - 24 ) = 573 - 73 + 24 = ( 573 - 73 ) + 24 = 500 + 24 = 524