Question

Cho \(\frac{x}{3}=\frac{y}{4}\) và \(\frac{y}{5}=\frac{z}{6}\) Tính M=\(\frac{2x+3y+4z}{3x+4y+5z}\)

Answer 1

Vì \(\frac{x}{3}\) = \(\frac{y}{4}\) => \(\frac{x}{15}\) = \(\frac{y}{20}\)

\(\frac{y}{5}\) = \(\frac{z}{6}\) => \(\frac{y}{20}\) = \(\frac{z}{24}\)

nên \(\frac{x}{15}\) = \(\frac{y}{20}\) = \(\frac{z}{24}\)

Đặt \(\frac{x}{15}\) = \(\frac{y}{20}\) = \(\frac{z}{24}\) = k

=> x = 15k; y = 20k và z = 24k

Thay vào M ta đc:

M = \(\frac{2.15k+3.20k+4.24k}{3.15k+4.20k+5.24k}\)

= \(\frac{30k+60k+96k}{45k+80k+120k}\)

= \(\frac{\left(30+60+96\right)k}{\left(45+80+120\right)k}\)

= \(\frac{186k}{245k}\) = \(\frac{186}{245}\)

Vậy M = \(\frac{186}{245}\).