B1:

a) = (8/15 + 7/15) + (7/4 + 5/4)

    = 15/15 + 12/4

    = 1 + 3

    = 4

b) = (16,88 + 3/12) + 9,76

     = 20 + 9,76

     = 29,76

c) = (17,16 + 82,84) + 72,84

    = 100 + 72,84

    = 172,84

B2:

2/3 + 4/5 = 10/15 + 12/15 = 22/15

a) \(\frac{8}{15}+\frac{7}{4}+\frac{7}{15}+\frac{5}{4}\)

\(=\left(\frac{8}{15}+\frac{7}{15}\right)+\left(\frac{7}{4}+\frac{5}{4}\right)\)

\(=\frac{15}{15}+\frac{12}{4}\)

\(=1+3=4\)

b) \(16,88+9,76+3,12\)

\(=\left(16,88+3,12\right)+9,76\)

\(=20+9,76=29,76\)

c) \(72,84+17,16+82,84\)

\(=\left(82,84+17,16\right)+72,84\)

\(=100+72,84=172,84\)

\(\frac{2}{3}+\frac{4}{5}=\frac{10}{15}+\frac{12}{15}=\frac{22}{15}\)

1,2 : 1,8 x 0,3=0,2

1,2 : 1,8 x 0,3 = ( 1,2 x 0,3 ) : 1,8

                     = 0,4 : 1,8

                     =  0,2

toán lớp 5 khó thế bạn

5/13 x 11/19 + 11/19 x 21/13

=11/19 x ( 5/13 + 21/13 )

=11/19 x 26/13

=11/19 x 2

=22/19

Tính bằng cách thuận tiện nhất :

\(3,6\cdot4\cdot0,125\cdot2,5\cdot8\)

\(=3,6\cdot\left(4\cdot2,5\right)\cdot\left(0,125\cdot8\right)\)

\(=3,6\cdot10\cdot1\)

\(=36\)

\(=\frac{74+69}{75+89}\)\(=\frac{10}{13}\)

\(\frac79\times\frac{13}{17}\times\frac{17}{13}=\frac79\times\left(\frac{13}{17}\times\frac{17}{13}\right)\)

\(=\frac79\times1=\frac79\)

cảm ơn nhé