a) 80 - 20 : 0,5 -3,12
= 80 - 40 - 3,12
= 40 - 3,12
= 36,88
b) ( 3,25 + 7,35 ) . ( 6 - 1,2 ) - 2,4
= 10,6 . 4,8 - 2,4
= 50,88 - 2,4
= 48,48
c) 35,16 - 44,84 :4 + 15,6 . 24
= 35,16 - 11,21 + 377,4
= 23,95 + 377,4
= 3801,35 

\(\dfrac{1}{4}-\dfrac{1}{3}+\dfrac{5}{12}\\ =\dfrac{3}{12}-\dfrac{4}{12}+\dfrac{5}{12}\\ =\dfrac{3-4+5}{12}\\ =\dfrac{4}{12}\\ =\dfrac{1}{3}\)

\(\left(1-\frac{1}{3}\right).\left(1-\frac{1}{6}\right).\left(1-\frac{1}{10}\right)...\left(1-\frac{1}{190}\right)\)

\(=\frac{2}{3}.\frac{5}{6}.\frac{9}{10}...\frac{189}{190}\)

\(=\frac{4}{6}.\frac{10}{12}.\frac{18}{20}...\frac{378}{380}\)

\(=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}...\frac{18.21}{19.20}\)

\(=\frac{1.2.3...18}{2.3.4...19}.\frac{4.5.6...21}{3.4.5...20}\)

\(=\frac{1}{19}.\frac{21}{3}\)

\(=\frac{1}{19}.7=\frac{7}{19}\)

\(\left(1-\frac{1}{3}\right).\left(1-\frac{1}{6}\right).\left(1-\frac{1}{10}\right)...\left(1-\frac{1}{190}\right)\)

\(=\frac{2}{3}.\frac{5}{6}.\frac{9}{10}....\frac{189}{190}\)

\(=\frac{4}{6}.\frac{10}{12}.\frac{18}{20}....\frac{378}{380}\)

\(=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}....\frac{18.21}{19.20}\)

\(=\frac{1.2.3....18}{2.3.4....19}.\frac{4.5.6...21}{3.4.5....20}\)

\(=\frac{1}{19}.\frac{21}{3}\)

\(=\frac{1}{19}.7=\frac{7}{19}\)

Ủng hộ mk nha !!! ^_^

\(-23.63+23.21-58.23\)
\(=-23.\left(63+21-58\right)\)
\(=-23.26\)
\(=-598\)
k mik nha

nhung lai co 2 so 23 va 1 so -23 nen lam the la sai

Sao cau lai ghi la ko mik nha la j vay

a, 35,16-44,84:4+15,6.24

=35,16-11.21+374,4

=398,35

b, Thay a=20,11 vào 2,75.a+7,25.a. Ta có:

2,75.20,11+7,25.20,11

=20,11.(2,75+7,25)

=20,11.10

=201,11

30-[50-(9-4)²]+2015⁰

=30-[50-5²]+2015⁰

=30-[50-25]+2015⁰

=30-25+2015⁰

=30-25+1

=5+1

=6