Tính hợp lí nhất có thể

Bài 4: $\frac32-[\frac{-5}4-(\frac12+\frac68)]$ = $\frac32 - [\frac{-5}4 - (\frac{3}{4})]$ = $\frac32 - [\frac{-5}4 - \frac34]$ = $\frac32 - [\frac{-2}4]$ = $\frac32 - [-\frac12]$ = $\frac32 + \frac12$ = $\frac52$ = 2.5 Bài 5: $\frac97-[\frac12]$ = $\frac97 - \frac27$ = $\frac57$ = 0.7142857142857143 Bài 20: 1) $(7-\frac15+\frac13)-(6+\frac95+\frac43)$ = $(7-\frac{3}{15}+\frac{5}{15}) - (6+\frac{45}{15}+\frac{20}{15})$ = $(7+\frac{2}{15}) - (6+\frac{65}{15})$ = $\frac{105}{15}+\frac{2}{15} - \frac{90}{15}-\frac{65}{15}$ = $\frac{107}{15} - \frac{155}{15}$ = $-\frac{48}{15}$ = -3.2 2) $(\frac12-\frac13)-(\frac53-\frac32)+(\frac73-\frac52)$ = $(\frac{3}{6}-\frac{2}{6}) - (\frac{10}{6}-\frac{9}{6}) + (\frac{21}{6}-\frac{15}{6})$ = $\frac{1}{6} - \frac{1}{6} + \frac{6}{6}$ = $1$ 3) $(3-\frac14+\frac23)-(5-\frac13-\frac65)-(6-\frac74+\frac32)$ = $(3-\frac{1}{4}+\frac{8}{12}) - (5-\frac{4}{12}-\frac{10}{12}) - (6-\frac{28}{12}+\frac{18}{12})$ = $(3+\frac{7}{12}) - (5-\frac{14}{12}) - (6-\frac{10}{12})$ = $\frac{36}{12}+\frac{7}{12} - \frac{60}{12}+\frac{14}{12} - \frac{72}{12}+\frac{10}{12}$ = $\frac{43}{12} - \frac{46}{12} + \frac{-62}{12}$ = $-\frac{65}{12}$ = -5.416666666666667 5) $(\frac53-\frac37+9)-(2+\frac57-\frac23)+(\frac87-\frac43-10)$ = $(\frac{15}{9}-\frac{21}{63}+9) - (2+\frac{35}{63}-\frac{42}{63}) + (\frac{56}{63}-\frac{27}{63}-10)$ = $(\frac{15}{9}-\frac{1}{3}+9) - (2+\frac{35}{63}-\frac{42}{63}) + (\frac{56}{63}-\frac{27}{63}-10)$ = $(\frac{5}{3}-\frac{1}{3}+9) - (2+\frac{-7}{63}) + (\frac{29}{63}-10)$ = $(\frac{4}{3}+9) - (2-\frac{7}{63}) + (\frac{29}{63}-10)$ = $\frac{40}{12}+\frac{108}{12} - \frac{24}{12}+\frac{7}{63} + \frac{29}{63}-\frac{120}{6}$ = $\frac{148}{12} - \frac{17}{12} - \frac{720}{63}$ = $\frac{131}{12} - \frac{720}{63}$ = $10.916666666666666 - 11.428571428571429$ = $-0.5119047619047625$