lisa is 50. she is twice as old as her little brother sam. sam is 3 times younger than their oldest sibling Brad. How old are Brad and Sam?

Let the ages of these three persons be represented by L, S and B. Then,

L=2S, and B/3=S.

With L=50, 50=2S, and so S = 25.

Since B/3=S, B=3S, so that B here is 75.

Lisa is 50, Brad is 75 and Sam is 25 (years of age).

Lisa is 50 years

Sam is 50 / 2 = 25 years

Brad is 25 * 3 = 75 years