Algebraic method substitution method)

Question

solve by substitution method 0.4x+0.3y=1.7 and 0.7x+0.2y=0.8

Answer 1

0.4x + 0.3y = 1.7 ----(1)

0.7x + 0.2y = 0.8 -----(2)

from (2) we get y = 0.8 - 0.7x / 0.2

substitute y = 0.8 - 0.7x/0.2 in equation (1), we get 

0.4x + 0.24 - 0.21x / 0.2 = 1.7

⇒ 0.08x + 0.24 - 0.21x = 0.34

⇒ -0.13x = 0.34 - 0.24 = 0.10 

⇒ x = 0.10 / - 0.13 = -10 / 13

∴ y = \(\frac{0.8-0.7\times\frac{-10}{13}}{0.2}\) 

= \(\frac{8+\frac{70}{13}}{2}=\frac{174}{26}=\frac{87}{13}\)