Tìm , biết : a) b) c)

a) Vậy . b) Vậy . c) Vậy .

Bài 116* (Sách bài tập - tập 2 - trang 32)

Gửi bởi: Sách Giáo Khoa Vào 26 tháng 12 2018 lúc 11:17:09

Tìm \(y\), biết :

a) \(y+30\%y=-1,3\)

b) \(y-25\%y=\dfrac{1}{2}\)

c) \(3\dfrac{1}{3}y+16\dfrac{3}{4}=-13,25\)

a) \(y+30\%y=-1.3\)

\(y+\dfrac{3}{10}y=\dfrac{-13}{10}\)

\(y\left(1+\dfrac{3}{10}\right)=\dfrac{-13}{10}\)

\(y\left(\dfrac{10}{10}+\dfrac{3}{10}\right)=\dfrac{-13}{10}\)

\(y\cdot\dfrac{13}{10}=\dfrac{-13}{10}\)

\(y=\dfrac{-13}{10}:\dfrac{13}{10}\)

\(y=\dfrac{-13}{10}\cdot\dfrac{10}{13}\)

\(y=-1\)

Vậy \(y=-1\).

b) \(y-25\%y=\dfrac{1}{2}\)

\(y-\dfrac{1}{4}y=\dfrac{1}{2}\)

\(y\left(1-\dfrac{1}{4}\right)=\dfrac{1}{2}\)

\(y\left(\dfrac{4}{4}-\dfrac{1}{4}\right)=\dfrac{1}{2}\)

\(y\cdot\dfrac{3}{4}=\dfrac{1}{2}\)

\(y=\dfrac{1}{2}:\dfrac{3}{4}\)

\(y=\dfrac{1}{2}\cdot\dfrac{4}{3}\)

\(y=\dfrac{2}{3}\)

Vậy \(y=\dfrac{2}{3}\).

c) \(3\dfrac{1}{3}y+16\dfrac{3}{4}=-13.25\)

\(\dfrac{10}{3}y+\dfrac{67}{4}=\dfrac{-53}{4}\)

\(\dfrac{10}{3}y=\dfrac{-53}{4}-\dfrac{67}{4}\)

\(\dfrac{10}{3}y=-30\)

\(y=-30:\dfrac{10}{3}\)

\(y=-30\cdot\dfrac{3}{10}\)

\(y=-9\)

Vậy \(y=-9\).