Question

Bài 442: Tính hợp lý: 

1. 1/3 . 4/5 + 1/3 . 6/5 - 1/3

2. 3/7 . 9/26 - 1/14 . 1/13 

3. 15(1/5 - 7/15 + 17/3)

4. 38(2và1/19 - 5và7/38)

5. 75( - 4/25 + 7và1/15 - 5và7/75)

 

Answer 1

\(1)\frac{1}{3}.\frac{4}{5}+\frac{1}{3}.\frac{6}{5}-\frac{1}{3}\)

\(=\frac{1}{3}\left(\frac{4}{5}+\frac{6}{5}\right)\)

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

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

Answer 2

\(1)\)\(\frac{1}{3}.\frac{4}{5}+\frac{1}{3}.\frac{6}{5}-\frac{1}{3}\)

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}-1\right)\)

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}-\frac{5}{5}\right)\)

\(=\frac{1}{3}.1\)

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

\(2)\)\(\frac{3}{7}.\frac{9}{26}-\frac{1}{14}.\frac{1}{13}\)

\(=\frac{1}{7}.\frac{27}{26}-\frac{1}{7}.\frac{1}{26}\)

\(=\left(\frac{27}{26}-\frac{1}{26}\right).\frac{1}{7}\)

\(=1.\frac{1}{7}\)

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

\(3)\)\(15\left(\frac{1}{5}-\frac{7}{15}+\frac{17}{3}\right)\)

\(=3-7+85\)

\(=81\)

\(4)\)\(38\left(2\frac{1}{19}-5\frac{7}{38}\right)\)

\(=38\left(\frac{39}{19}-\frac{197}{38}\right)\)

\(=78-197\)

\(=-119\)

\(5)\)\(75\left(\frac{-4}{25}+7\frac{1}{15}-5\frac{7}{75}\right)\)

\(=75\left(\frac{-4}{25}+\frac{106}{15}-\frac{382}{75}\right)\)

\(=-12+530-382\)

\(=136\)

Ddaeng

Answer 3

1, \(\frac{1}{3}.\frac{4}{5}+\frac{1}{3}.\frac{6}{5}-\frac{1}{3}\)

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}\right)-\frac{1}{3}\)

\(=\frac{1}{3}.2-\frac{1}{3}\)

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

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

2, \(\frac{3}{7}.\frac{9}{26}-\frac{1}{14}.\frac{1}{13}\)

\(=\frac{1}{7}.3.\frac{9}{26}-\frac{1}{7}.\frac{1}{2}.\frac{1}{13}\)

\(=\frac{1}{7}.\frac{27}{26}-\frac{1}{7}.\frac{1}{26}\)

\(=\frac{1}{7}.\left(\frac{27}{26}-\frac{1}{26}\right)\)

\(=\frac{1}{7}.1\)

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

3, \(15.\left(\frac{1}{5}-\frac{7}{15}+\frac{17}{3}\right)\)

\(=15.\frac{1}{5}-15.\frac{7}{15}+15.\frac{17}{3}\)

\(=3-7+85\)

\(=81\)

4, \(38.\left(2\frac{1}{19}+5\frac{7}{38}\right)\)

\(=38.\left(\frac{39}{19}+\frac{197}{38}\right)\)

\(=38.\frac{39}{19}+38.\frac{197}{38}\)

\(=78+197\)

\(=275\)

5, \(75.\left(\frac{-4}{25}+7\frac{1}{15}-5\frac{7}{75}\right)\)

\(=75.\left(\frac{-4}{25}+\frac{106}{15}-\frac{382}{75}\right)\)

\(=75.\frac{-4}{25}+75.\frac{106}{15}-75.\frac{382}{75}\)

\(=-12+530-382\)

\(=136\)