Giải bài 74 trang 49 sách bài tập Toán 6 – Cánh Diều Tập 2

Đề bài

Tính một cách hợp lí:

a) \(0,125.0,694.80;\)

b) \(721,9.99 + 721 + 0,9;\)

c) \(28.7,32 - 7,32:0,125;\)

d) \(914,75:5 + 211,2:5 - 101,95:5;\)

e) \(\left( { - 1,4} \right):\left( { - 3} \right) + \left( { - 5,8} \right):\left( { - 3} \right);\)

g) \(5,17:\left( { - 1,3} \right) + 1,43.1,1 + 3{\rm{ }}.0,143{\rm{ }}7,83:\left( { - {\rm{ }}1,3} \right).\)

Lời giải chi tiết

a) \(0,125.0,694.80\)

\(= \left( {0,125.80} \right).0,694\)

\(= 10.0,694 = 6,94\)

b) \(721,9.99 + 721 + 0,9 \)

\(= 721,9.99 + (721 + 0,9) \)

\(= 721,9.99 + 721,9\)

\(= 721,9.99 + 721,9.1\)

\(= 721,9.\left( {99 + 1} \right)\)

\(= 721,9.100 = 72190\)

c) \(28.7,32 - 7,32:0,125\)

\(= 28.7,32 - 7,32:\frac{{125}}{{1000}} \)

\(= 28.7,32 - 7,32:\frac{1}{8}\)

\( = 28.7,32 - 7,32.8 \)

\(= 7,32.\left( {28 - 8} \right)\)

\(= 7,32.20 = 146,4\)

d) \(914,75:5 + 211,2:5 - 101,95:5 \)

\(= \left( {914,75 + 211,2 - 101,95} \right):5\)

\(= \left[ {\left( {914,75 + 211,2} \right) - 101,95} \right]:5\)

\(= \left( {1125,95 - 101,95} \right):5 \)

\(= 1024:5 \)

\(= 204,8\)

e) \(\left( { - 1,4} \right):\left( { - 3} \right) + \left( { - 5,8} \right):\left( { - 3} \right)\)

\(= \left[ {\left( { - 1,4} \right) + \left( { - 5,8} \right)} \right]:\left( { - 3} \right) \)

\(= \left( { - 7,2} \right):\left( { - 3} \right) \)

\(= 2,4\)

g) \(5,17:\left( { - 1,3} \right) + 1,43.1,1 + 39.0,143 + 7,83:\left( { - {\rm{ }}1,3} \right)\)

\( = 5,17:\left( { - 1,3} \right) + 7,83:\left( { - {\rm{ }}1,3} \right) + 1,43.1,1 + 39.0,143\)

\( = \left( {5,17 + 7,83} \right):\left( { - {\rm{ }}1,3} \right) + 1,43.1,1 + 39.0,143\)

\( = \left( {5,17 + 7,83} \right):\left( { - {\rm{ }}1,3} \right) + 1,43.1,1 + 3,9.1,43\)

\( = 13:\left( { - {\rm{ }}1,3} \right) + 1,43.\left( {1,1 + 3,9} \right)\)

\( =  - 10 + 1,43.5\)

\( =  - 10 + 7,15\)

\( =  - 2,85\)