Question

Дано 4а + 6b = 20 и 6а + 4b = 40
Чему равно среднее арифметическое а и b?

Answer 1

$large \ left{begin{matrix} 4a+6b=20\ 6a+4b=40 end{matrix}right.left{begin{matrix} 2a+3b=10\ 6a+4b=40 end{matrix}right. left{begin{matrix} 2a=10-3b\ 30-9b+4b-40=0 end{matrix}right. left{begin{matrix} 2a=10-3b\ 5b=-10 end{matrix}right. left{begin{matrix} a=8\ b=-2 end{matrix}right.\\ {a+bover2}={8-2over2}=3$