Lời giải:
\(\frac{20^4.15^5}{12^5.25^4}=\frac{(2^2.5)^4.(3.5)^5}{(2^2.3)^5.(5^2)^4}=\frac{2^8.5^4.3^5.5^5}{2^{10}.3^5.5^8}\)

\(=\frac{2^8.5^9.3^5}{2^{10}.3^5.5^8}=\frac{2^8.5^8.5.3^5}{2^8.2^2.3^5.5^8}=\frac{5}{2^2}=\frac{5}{4}\)

a: =8-6=2

b: =30(55+46-1)=3000

a) 8 + 2. ( − 3 ) = 8 + ( - 6 ) = 8 - 6 = 2 
b) 30.55 + 30.46 – 2.15

= 30 . 55 + 30 . 46 - 30

= 30 . ( 55 + 46 - 1 )

= 30 . 100 = 3000
c) 4.15 − [ 144 − ( 12 − 4 )² ]

= 4 . 15 - [ 144 - 8² ]

= 4 .15 - [ 144 - 64 ] 

= 60 - 80

= - 20

\(A=1-\left(\frac{3}{2.10}+\frac{3}{4.15}+\frac{3}{6.20}+....+\frac{3}{198.500}\right)\)

  \(=1-\frac{3}{2.5}\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\right)\)

   \(=1-\frac{3}{25}\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\right)\)

   \(=1-\frac{3}{25}\left(1-\frac{1}{100}\right)\)

\(=1-\frac{3.99}{25.100}=\frac{703}{1000}\)

\(3.\left(-5\right)^2+2.\left(-15\right)-20=-15.\left(-5\right)+2.\left(-5\right).3+4.\left(-5\right)\)

                                                         \(=-5.\left(-15+2.3+4\right)\)

                                                         \(=-5.\left(-5\right)\)

                                                         \(=25\)

các bạn giúp mik vs

\(\left(-216\right):9+7^5:7^3-\left(-4\right)^2.5\)

\(\Leftrightarrow\left(-24\right)+7^2-16\)

\(\Leftrightarrow\left(-24\right)+49-16\)

\(\Leftrightarrow25-16\)

\(\Leftrightarrow9\)