\(B\left(5\right)=0;5;10;15;...;90;95;100\)

\(B\left(9\right)=0;9;18;27;...;90;99\)

\(B\left(20\right)=0;20;40;...;80;100\)

\(B\left(12\right)=0;12;24;...;96\)

\(a,\dfrac{11}{12}-\left(\dfrac{2}{5}+x\right)=\dfrac{2}{3}\)

\(\dfrac{2}{5}+x=\dfrac{11}{12}-\dfrac{2}{3}\)

\(\dfrac{2}{5}+x=\dfrac{1}{4}\)

\(x=\dfrac{1}{4}-\dfrac{2}{5}\)

\(x=\dfrac{-3}{20}\)

Vậy \(x=-\dfrac{3}{20}\)

___________________

\(b,2x\left(x-\dfrac{1}{7}\right)=0\)

\(2x=0\) hoặc \(x-\dfrac{1}{7}=0\)

\(x=0\) hoặc \(x=\dfrac{1}{7}\)

Vậy \(x=0\) hoặc \(x=\dfrac{1}{7}\)

____________________

\(c,\dfrac{3}{4}+\dfrac{1}{4}:x=\dfrac{2}{5}\)

\(\dfrac{1}{4}:x=\dfrac{2}{5}-\dfrac{3}{4}\)

\(\dfrac{1}{4}:x=\dfrac{-7}{20}\)

\(x=\dfrac{1}{4}:-\dfrac{7}{20}\)

\(x=-\dfrac{5}{7}\) 

Vậy \(x=-\dfrac{5}{7}\)

\(a,2.3^{^x}=162\)

\(3^{^x}=162:2\)

\(3^{^x}=81\)

\(3^{^x}=3^{^4}\)

\(x=4\)

_______________

\(b,2^x-15=17\)

\(2^x=17+15\)

\(2^x=32\)

\(2^x=2^5\)

\(x=5\)

_________________

\(c\left(7x-11\right)^3=2^5.5^2+200\)

\(\left(7x-11\right)^3=1000\)

\(\left(7x-11\right)^3=10^3\)

\(7x-11=10\)

\(7x=10+11\)

\(7x=21\)

\(x=21:7\)

\(x=3\)

\(a,\dfrac{3}{7}+\left(-\dfrac{5}{2}\right)+\left(-\dfrac{3}{5}\right)\)

\(=\dfrac{30}{70}+\dfrac{-175}{70}+\dfrac{-42}{70}=\dfrac{30+\left(-175\right)+\left(-42\right)}{70}=\dfrac{-187}{70}\)

________________________

\(b,\left(-\dfrac{4}{3}\right)+\left(-\dfrac{2}{5}\right)+\left(-\dfrac{3}{2}\right)\)

\(=\dfrac{-40}{30}+\dfrac{-12}{30}+\dfrac{-45}{30}=\dfrac{\left(-40\right)+\left(-12\right)+\left(-45\right)}{30}=\dfrac{-97}{30}\)

__________________________

\(c,\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\)

\(=\dfrac{56}{70}-\dfrac{-20}{70}-\dfrac{49}{70}=\dfrac{56-\left(-20\right)-49}{70}=\dfrac{27}{70}\)

________________________________

\(d,\dfrac{2}{3}-\left[\left(-\dfrac{7}{4}\right)-\left(\dfrac{1}{2}+\dfrac{3}{8}\right)\right]\)

\(=\dfrac{2}{3}-\left[\left(-\dfrac{7}{4}\right)-\dfrac{7}{8}\right]\)

\(=\dfrac{2}{3}-\dfrac{-21}{8}\)

\(=\dfrac{16}{24}-\dfrac{-63}{24}=\dfrac{16-\left(-63\right)}{24}=\dfrac{79}{24}\)

\(a)0,6+\dfrac{2}{-3}\)

\(\dfrac{3}{5}+\dfrac{-2}{3}=\dfrac{9}{15}+\dfrac{-10}{15}=\dfrac{9+\left(-10\right)}{15}=\dfrac{-1}{15}\)

____________________

\(b)\dfrac{1}{3}-\left(-0,4\right)\)

\(\dfrac{1}{3}-\left(-\dfrac{2}{5}\right)=\dfrac{5}{15}-\dfrac{-6}{15}=\dfrac{5-\left(-6\right)}{15}=\dfrac{11}{15}\)

_________________________

\(c)3,5.\left(-1\dfrac{2}{5}\right)\)

\(\dfrac{7}{2}.\left(-\dfrac{7}{5}\right)=-\dfrac{49}{10}\)

___________________________

\(d)-\dfrac{5}{23}:\left(-2\right)=-\dfrac{5}{23}.\left(-\dfrac{1}{2}\right)=\dfrac{5}{46}\)

\(2\times x-25=125\)

\(2\times x=125+25\)

\(2\times x=150\)

\(x=150:2\)

\(x=75\)

___________

\(120-3\times x=0\)

\(3\times x=120-0\)

\(3\times x=120\)

\(x=120:3\)

\(x=40\)

_____________

\(2\times x-11=23\)

\(2\times x=23+11\)

\(2\times x=34\)

\(x=34:2\)

\(x=17\)

\(g,2\left(x-51\right)=2.2^3+20\)

\(2\left(x-51\right)=36\)

\(x-51=36:2\)

\(x-51=18\)

\(x=18+51\)

\(x=69\)

_______________

\(h,450:\left(x-19\right)=50\)

\(x-19=450:50\)

\(x-19=9\)

\(x=9+19\)

\(x=28\)

_________________

\(i,4\left(x-3\right)=7^2-1^{10}\)

\(4\left(x-3\right)=48\)

\(x-3=48:4\)

\(x-3=12\)

\(x=12+3\)

\(x=15\)

________________

\(p,135-5\left(x+4\right)=35\)

\(5\left(x+4\right)=135-35\)

\(5\left(x+4\right)=100\)

\(x+4=100:5\)

\(x+4=20\)

\(x=20-4\)

\(x=16\)

__________________

\(q,25+3\left(x-8\right)=106\)

\(3\left(x-8\right)=106-25\)

\(3\left(x-8\right)=81\)

\(x-8=81:3\)

\(x-8=27\)

\(x=27+8\)

\(x=35\)

________________

\(r,3^2\left(x+4\right)-5^2=5.2^2\)

\(9\left(x+4\right)-25=20\)

\(9\left(x+4\right)=20+25\)

\(9\left(x+4\right)=45\)

\(x+4=45:9\)

\(x+4=5\)

\(x=5-4\)

\(x=1\)

\(d)89-\left(73-x\right)=20\)

\(73-x=89-20\)

\(73-x=69\)

\(x=73-69\)

\(x=4\)

_______________

\(e)\left(x+7\right)-25=13\)

\(x+7=13+25\)

\(x+7=38\)

\(x=38-7\)

\(x=31\)

_______________________

\(f)198-\left(x+4\right)=120\)

\(x+4=198-120\)

\(x+4=78\)

\(x=78-4\)

\(x=74\)

__________________

\(m)5\left(x-9\right)=350\)

\(x-9=350:5\)

\(x-9=70\)

\(x=70+9\)

\(x=79\)

_____________________

\(n)2x-49=5.3^2\)

\(2x-49=45\)

\(2x=45+49\)

\(2x=94\)

\(x=94:2\)

\(x=47\)

______________

\(o)200-\left(2x+6\right)=4^3\)

\(2x+6=200-64\)

\(2x+6=136\)

\(2x=136-6\)

\(2x=130\)

\(x=130:2\)

\(x=65\)

Câu cuối bạn làm sai rồi:)