Sis : you : bro
10 : 9 : ?
? ? : 27 : 29
We can get the 9 at the top to 27, by multiplying the whole row by 3 to get:
30 : 27 :?
? : 27 : 29
Your age matches (in the ratios or relation to your sis & bro) now 27 yrs in both ratio. Creating a single ratio, whereby multiplying the top row by 3 to get you to 27 & bottom row by 1 to get you to 27. Knowing when you're 27 in both cases, you know how old your sis & bro is
So, replace the ? with the number above or below it, creating a single ratio, where you are in common with both, by being 27 in both cases.
The ratio of sis : you : bro is now -
The ratio of sis : you : bro is now - 30: 27 : 29
To find what your age is we need to increase the ratio in the same amount to find your maximum age under 70.
So, if we were to double your age to 54, by multiplying your previous age of 27 by 2. We've got to do the same for your sis & bro too, they're aging with you.
We get :
We get :60 : 54 : 58
(30 x 2) : (27 x2) : (29 x2)
Keep increasing the ratio, to the point you're not above 70 years. Now, I'll multiply all ages by 3.
30: 27 : 29
(30 x 3) : ( 27 x 3) : (29 x 3)
We get:
We get:90 : 81 : 87
Right now, you're above the age of 70.
Thus, your maximum age must be 54, where you're under 70 years, but over 40 years.
Answer : 54 years
Hope this helps!