Question

Помогите пожалуйста решить задачу номер 5

Answer 1

В= 10x+y
Д= 10y+x

B/(x+y) -Д/(x+y) = x-y <=>
(B-Д)/(x+y) = x-y <=>
9(x-y)/(x+y) = x-y <=>
x+y =9

B/(x+y) *Д/(x+y) =B <=>
Д/(x+y)^2 =1 <=>
10y +x =(x+y)^2 <=>
10(9-x) +x =81 <=>
90 -9x =81 <=>
x= (90-81)/9 =1

y=9-1=8

Ответ: внуку 18 лет.