= 1 - 1/121                                                                                                                                                                                                           =     120/121

Các bạn trình bày rõ ràng cho mình nha!

A= 3/4 x 8/9 x 15/16 x...x99/100 x 120/121

A=3x8x15x...x99x121/4x9x16x...x100x121

A= 1 x 3 x 2 x 4 x 3 x 5 x ... x 9 x 11 x 10 x 12/ 2 x 2 x 3 x 3 x 4 x 4 x ... x 10 x 10 x 11 x 11

A= (1x2x3x...x9x10)x(3x4x5x...x11x12)/(2x3x4x...x10x11)x(2x3x4x...x10x11)

A=1x12/11x2

A=6/11

Vậy A=6/11

a)    \(\frac{3}{16}+\frac{4}{15}+\frac{5}{16}+\frac{1}{15}\)

\(=\left(\frac{3}{16}+\frac{5}{16}\right)+\left(\frac{4}{15}+\frac{1}{15}\right)\)

\(=\frac{1}{2}+\frac{1}{3}\)

\(=\frac{5}{6}\)

b)   \(\frac{6}{7}\times\frac{8}{15}\times\frac{7}{6}\times\frac{15}{16}\)

\(=\left(\frac{6}{7}\times\frac{7}{6}\right)\times\left(\frac{8}{15}\times\frac{15}{16}\right)\)

\(=1\times\frac{1}{2}=\frac{1}{2}\)

c)   \(\frac{19}{20}\times\frac{13}{21}+\frac{9}{20}\times\frac{8}{21}\)

\(=\frac{19\times13}{20\times21}+\frac{9\times8}{20\times21}\)

\(=\frac{247}{420}+\frac{72}{420}\)

\(=\frac{319}{420}\)

còn phần D đâu bn 

tích cho chị nha

 câu a)     = 5/6

 câu b = 1/2

 câu c = 319/420

\(\left(1\frac{1}{7}\right)\left(1\frac{1}{8}\right)\left(1\frac{1}{9}\right)...\left(1\frac{1}{50}\right)\)

\(=\frac{8}{7}.\frac{9}{8}.\frac{10}{9}...\frac{51}{50}\)

\(=\frac{8.9.10...51}{7.8.9...50}\)

\(=\frac{51}{7}\)

\(=\frac{8}{7}\times\frac{9}{8}\times\frac{10}{9}\times...\times\frac{51}{50}\)

\(=\frac{51}{7}\)

\(1\frac{1}{7}.1\frac{1}{8}.1\frac{1}{9}.....1\frac{1}{50}\)

\(=\frac{8}{7}.\frac{9}{8}.\frac{10}{9}.....\frac{51}{50}\)

\(=\frac{51}{7}\)