Giải bài 74 trang 49

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) $5,17:\left(-1,3\right)+1,43.1,1+3.0,1437,83:\left(-1,3\right).$

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) $5,17:\left(-1,3\right)+1,43.1,1+39.0,143+7,83:\left(-1,3\right)$

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

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

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

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

$=-10+1,43.5$

$=-10+7,15$

$=-2,85$