Question

Answer 1

Bài 3:

a: 365,8-x=89,7:1,3

=>365,8-x=69

=>x=365,8-69=296,8

b: 52,7+7,5x5=(x+175):5+30

=>(x+175):5+30=52,7+37,5=90,2

=>(x+175):5=60,2

=>\(x+175=60,2\times5=301\)

=>x=301-175

=>x=126

c: \(640-\left(15\times24-x\right):0,25=100:\frac14\)

=>\(640-\left(360-x\right)\times4=400\)

=>4x(360-x)=640-400=240

=>360-x=240:4=60

=>x=360-60

=>x=300

d: \(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}\right)\times x=1\)

=>\(\frac{x}{2}\times\left(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}\right)=1\)

=>\(\frac{x}{2}\times\left(\frac13-\frac15+\frac15-\frac17+\frac17-\frac19\right)=1\)

=>\(\frac{x}{2}\times\left(\frac13-\frac19\right)=1\)

=>\(\frac{x}{2}\times\frac29=1\)

=>\(\frac{x}{9}=1\)

=>x=9

Bài 2:

a: \(27,84\times30+27,84\times71-27,84\)

\(=27,84\times\left(30+71-1\right)\)

\(=27,84\times100=2784\)

b: 200,6+2x200,6+3x200,6+4x200,6

=200,6x(1+2+3+4)

=200,6x10

=2006

c: \(\frac14\times\frac25\times\frac43\times\frac52\times\frac37\)

\(=\frac14\times\frac43\times\frac37\times\frac25\times\frac52=\frac17\)

d: \(\left(1-\frac12\right)\times\left(1-\frac13\right)\times\ldots\times\left(1-\frac{1}{20}\right)\)

\(=\frac12\times\frac23\times...\times\frac{19}{20}\)

\(=\frac{1}{20}\)

e: \(128\times72+14\times256\)

\(=128\times\left(72+14\times2\right)\)

\(=128\times100=12800\)