a: =1h15p+4h45p+2h24p+3h36p

=6h+6h

=12h

b: =2,5h+4,5h+5h

=7h+5h

=12h

c: =10h-8h=2h

\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)

\(\frac{37}{35}:\frac{5}{4}:\frac{74}{25}\)

\(=\frac{37}{35}:\left(\frac{5}{4}\times\frac{74}{25}\right)\)

\(=\frac{37}{35}:\frac{37}{10}\)

\(=\frac{2}{7}\)

\(\frac{37}{35}:\frac{5}{4}:\frac{74}{25}\)

=\(\frac{37}{35}x\frac{4}{5}x\frac{25}{74}\)

\(=\left(\frac{37}{35}x\frac{25}{74}\right)x\frac{4}{5}\)

\(=\frac{1}{7}x\frac{5}{2}x\frac{4}{5}\)

\(=\frac{1x5x2x2}{7x2x5}\)

\(=\frac{2}{7}\)

17/35 nhân 9/5 nhân 4/5 

= 17/35 nhân ( 9/5 nhân 4/5 )

= 17/35 nhân 13/5

=  221/175

Tính bằng cách thuận tiện nhất 3/5 + 3/8 + 2/5 + 5/8 bằng

35 x 3/4 + 45,5 x 75/100 + 20,5 x 75% - 0,75

= 35 x 0,75 + 45,5 x 0,75 + 20,5 x 0,75 - 0,75 x 1

= ( 35 + 45,5 + 20,5 - 1 ) x 0,75

= 100 x 0,75

= 75

1 Tính
7/12 - 2/7 + 1/12= (7/12-1/12)+2/7=6/12+2/7=1/2+2/7=7/14+4/14=11/14
12/17-5/17-4/17= 12-5-4/17=3/17

2a, 7/11+3/4+4/11+1/4= (7/11+4/11)+3/4+1/4=11/11+4/4=1+1=2
b)72/99-28/99-14/99= (72-28-14)/99=30/99=10/33

c)69,78+35,97+30,22= (69,78+30,22)+35,97=100+35,97=135,97

d) 83,45-30,98-42,47=83,45-(30,98+42,47)=83,45-73,45=10