The present age of your elder sister who is twice the age of your younger sistet 3 years ago.

Question

Mathematical model

Answer 1

present age of elder sister is twice the age of younger sister 3 years ago

E>Y

E =2(Y-3)

E = 2Y -6

Younger is at least 3 years old

but if Y =3 then E =0, so Elder is at least 4

if E=4, Y = 5, but E>Y

Let E=Y then Y=2Y -6, Y=6, For E>Y, the Younger sister is over 6 years old

Y=7, then E=8

IF ages are integers, and you are the middle age between 7 and E

then Youngest is at least 7 years old,

you are at least 8, and the Elder sister is at least 9 years