13+x=91

x=91-13

x=78

y-45=55

y=55+45

y=100

x+y=78+100=178

= 855x45+ 855x55

= 855x( 45+55)

=855x100

=85500

a)45/120=3/8=y/8->y=3

3/8=33/88->x=88

x = 4323 trong số 4500

y = 4345 ( có một số bảo bối 2 chức năng )

z = Tất cả ^_^

Đoán z  thôi

x+45=45-45+55:55

x+45=0+1

x+45=1

x=1-45

x=-44

k nhé mk vừa k bn rùi

x + 45 = 45 - 45 + 55 : 55

x + 45 = 45 - 45 + 1

x + 45 = 0 + 1 

x + 45 = 1

        x = 1 - 45

        x = -44

bài toán này hình như sai

55 x (45 + 55)

= 55 x 100

= 5500

55 x 45 + 55 x 55 

= 55 x ( 45 + 55 )

= 55 x 100

= 5500

55 x 45 + 55 x 55

= 55 x (45 + 55)

= 55 x 100

= 5500 nha 

\(\dfrac{x-45}{55}+\dfrac{x-47}{53}=\dfrac{x-55}{45}+\dfrac{x-53}{47}\)

\(\Leftrightarrow\left(\dfrac{x-45}{55}-1\right)+\left(\dfrac{x-47}{53}-1\right)=\left(\dfrac{x-55}{45}-1\right)+\left(\dfrac{x-53}{47}-1\right)\)

\(\Leftrightarrow\dfrac{x-100}{55}+\dfrac{x-100}{53}=\dfrac{x-100}{45}+\dfrac{x-100}{47}\)

\(\Leftrightarrow\dfrac{x-100}{55}+\dfrac{x-100}{53}-\dfrac{x-100}{45}-\dfrac{x-100}{47}=0\)

\(\Leftrightarrow\left(x-100\right)\left(\dfrac{1}{55}+\dfrac{1}{53}-\dfrac{1}{45}-\dfrac{1}{47}\right)=0\)

Do \(\dfrac{1}{55}+\dfrac{1}{53}-\dfrac{1}{45}-\dfrac{1}{47}\ne0\) nên x - 100 = 0 <=> x = 100

y×95-y×55+y×60=20900

(95-55+60)×y=20900

100×y=20900

y=20900÷100

y=209