Lời giải:
a.

$=(15+1-16)+(17+1-18)+17=16-16+18-18+17=0+0+17=17$

b. Đề hiển thị lỗi. Bạn xem lại.

Lời giải:
Số số hạng của $A$: $\frac{102-5}{1}+1=98$

$A=\frac{(102+5).98}{2}=5243$

Số số hạng của $B$: $\frac{50-2}{3}+1=17$

$B=\frac{(50+2).17}{2}=442$

Số số hạng của $C$: $\frac{100-5}{5}+1=20$

$C=\frac{(100+5).20}{2}=1050$

\(A=5+6+7+8+...+102=\left(102+5\right).\left(\dfrac{102-5}{1}+1\right)=10486\)

\(B=2+5+8+11+...+47+50=\left(50+2\right).\left(\dfrac{50-2}{3}+1\right)=884\)

\(C=5+10+15+20+25+...+100=\left(100+5\right).\left(\dfrac{100-5}{5}+1\right)=2100\)

ta có : (ghi lại đề)

=6+12+18+24+30/3+6+9+12+15

=2*(3/3+6/6+9/9+12/12+15/15)

=2*(1+1+1+1+1)

=2*5=10

chúc main học tốt nhé

Bài 5 :\(a,\left(8576-535\right)-8576\)

\(=8576-535-8576\)

\(=\left(8576-8576\right)-535\)

\(=0-535\)

\(=-535\)

\(b,\left(-7105\right)-\left(155-7105\right)\)

\(=-7105-155+7105\)

\(=\left(-7105+7105\right)-155\)

\(=0-155\)

\(=-155\)

\(c,8715+\left(1345+8715\right)\)

\(=8715+1345+8715\)

\(=8715\times2+1345\)

\(=17430+1345\)

\(=18775\)

\(d,\left(35-815\right)-\left(795-65\right)\)

\(=35-815-795+65\)

\(=\left(35+65\right)-\left(815+795\right)\)

\(=100-1610\)

\(=-1510\)

Bài 6 : \(a,25-\left(30+x\right)=x-\left(27-8\right)\)

                    \(25-30-x=x-19\)

                              \(-x-x=-19-25+30\)

                                    \(-2x=-14\)

                                          \(x=7\)

\(b,\left(x-2\right)-15=\left(20-7\right)-\left(18+x\right)\)

         \(x-2-15=13-18-x\)

                    \(x+x=13-18+2+15\)

                          \(2x=12\)

                             \(x=6\)

Ta có:\(\frac{3}{15}=\frac{3.2}{15.2}\)

\(\Rightarrow\frac{3}{15}=\frac{1}{5}\)

\(\Rightarrow\frac{6}{18}=\frac{1}{3}\)

\(\Rightarrow\frac{3}{15}< \frac{6}{18}\)

a) 3/15=6/30<6/18 suy ra 3/15<6/18

b)1/2=0.5

3/15=0.2

4/6=0.6

suy ra 4/5>1/2>3/15

a) ta có: \(\frac{3}{15}=\frac{1}{5};\frac{6}{18}=\frac{1}{3}\)

\(\Rightarrow\frac{1}{5}< \frac{1}{3}\Rightarrow\frac{3}{15}< \frac{6}{18}\)

b) ta có: \(\frac{1}{2}=\frac{15}{30};\frac{3}{15}=\frac{1}{5}=\frac{6}{30};\frac{4}{6}=\frac{2}{3}=\frac{20}{30}\)

\(\Rightarrow\frac{6}{30}< \frac{15}{30}< \frac{20}{30}\)

\(\Rightarrow\frac{3}{15}< \frac{1}{2}< \frac{4}{6}\)

c) ta có: \(\frac{1345}{1612}=0,8;\frac{4524}{4625}=0,9\)

\(\Rightarrow0,8< 0,9\Rightarrow\frac{1345}{1612}< \frac{4524}{4625}\)

d) ta có: \(\frac{7}{5}>1;\frac{6}{9}=\frac{2}{3}< 1;\frac{4}{3}>1;\frac{7}{15}< 1;1=1\)

mà \(\frac{7}{5}=\frac{21}{15};\frac{4}{3}=\frac{20}{15}\)

\(\Rightarrow\frac{21}{15}>\frac{20}{15}\Rightarrow\frac{7}{5}>\frac{4}{3}\)

mà \(\frac{6}{9}=\frac{2}{3}=\frac{5}{15}\)

\(\Rightarrow\frac{10}{15}>\frac{7}{15}\Rightarrow\frac{6}{9}>\frac{7}{15}\)

\(\Rightarrow\frac{7}{5}>\frac{4}{3}>1>\frac{6}{9}>\frac{7}{15}\)

 a,  \(\dfrac{5\times11\times15\times18}{6\times15\times22\times10}\)

= \(\dfrac{5\times11\times15\times6\times3}{6\times15\times11\times2\times2\times5}\)

= \(\dfrac{5\times11\times15\times6}{5\times11\times15\times6}\) \(\times\) \(\dfrac{3}{2\times2}\)

= 1 \(\times\) \(\dfrac{3}{4}\)

= \(\dfrac{3}{4}\)

b, \(\dfrac{7}{12}\) \(\times\) \(\dfrac{3}{5}\) + \(\dfrac{3}{5}\) \(\times\) \(\dfrac{5}{12}\)

= \(\dfrac{3}{5}\) \(\times\) ( \(\dfrac{7}{12}+\dfrac{5}{12}\))

= \(\dfrac{3}{5}\) \(\times\) \(\dfrac{12}{12}\)

= \(\dfrac{3}{5}\) \(\times\) 1 

= \(\dfrac{3}{5}\)