Question 891159
let the ages of the 3 kids be a, b, c
:
Write an equation for each statement
:
The ages of three siblings total 21 years. 
a + b + c = 21
The middle child is one year older than the youngest,
b = c + 1
 and the eldest is three times as old as the youngest.
a = 3c
:
Om the first equation replace a with 3c and b with (c+1)
3c + (c+1) + c = 21
5c = 21 - 1
c = 20/5
c = 4 yrss old
:
I'll let you find a and b, check your solutions in the 1st equation