\(\left(25\%\cdot x-7,25\right)+4,25=10\)

=>\(x\cdot0,25-3=10\)

=>\(x\cdot0,25=13\)

=>\(x=\dfrac{13}{0,25}=52\)

Chọn C

triu tui moi hoc lop 5

\(\begin{array}{l}a)x + 7,25 = 15,75\\x = 15,75 - 7,25\\x = 8,5\end{array}\)

Vậy x = 8,5

\(\begin{array}{l}b)\left( { - \frac{1}{3}} \right) - x = \frac{{17}}{6}\\\left( { - \frac{1}{3}} \right) - \frac{{17}}{6} = x\\\frac{{ - 2}}{6} - \frac{{17}}{6} = x\\\frac{{ - 19}}{6} = x\\x = \frac{{ - 19}}{6}\end{array}\)

Vậy \(x = \frac{{ - 19}}{6}\)

Chú ý: A = B và B = A là tương đương nhau

12/60+(-1/5-2,75)-0,25

=12/60+(-2,95)-0,25

= -3

HT

\(0,25\cdot\dfrac{7}{15}-\dfrac{1}{4}\cdot\left(-\dfrac{8}{15}\right)+2,75\)

\(=\dfrac{1}{4}\cdot\left(\dfrac{7}{15}+\dfrac{8}{15}\right)+2,75\)

\(=\dfrac{1}{4}\cdot1+2,75\)

\(=0,25+2,75\\ =3\)

hoặc 2,75 = \(\frac{275}{100}=\frac{11}{4}\)

Quy tắc: bỏ dấu phẩy và lấy số đó chia cho lũy thừa của 10;  có  bao nhiêu chữ số sau dấu phẩy thì có bấy nhiêu chữ số 0

$b)B=(\frac{3}{4}-0,6+\frac{3}{7}+\frac{3}{13}):(\frac{11}{13}+\frac{11}{7}-2,2+2,75)$

$=(\frac{3}{4}-\frac{3}{5}+\frac{3}{7}+\frac{3}{13}):(\frac{11}{13}+\frac{11}{7}-\frac{11}{5}+\frac{11}{4})$

$=3(\frac{1}{4}-\frac{1}{5}+\frac{1}{7}+\frac{1}{13}):11(\frac{1}{13}+\frac{1}{7}-\frac{1}{5}+\frac{1}{4})$

\(\dfrac{\dfrac{3}{4}-0,6+\dfrac{3}{7}+\dfrac{3}{13}}{\dfrac{11}{13}+\dfrac{11}{7}-2,2+2,75}\\ =\dfrac{\dfrac{3}{4}-\dfrac{3}{5}+\dfrac{3}{7}+\dfrac{3}{13}}{\dfrac{11}{13}+\dfrac{11}{7}-\dfrac{11}{5}+\dfrac{11}{4}}\\ =\dfrac{3\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{7}+\dfrac{1}{13}\right)}{11\left(\dfrac{1}{13}+\dfrac{1}{7}-\dfrac{1}{5}+\dfrac{1}{4}\right)}\\ =\dfrac{3}{11}\)