Question 829889
Let a = The speaker's age.
let b = one sister's age
let c = the other sister's age
:
Write an equation for each statement
:
I have two sisters.
 I am three times older than one of my sisters,
a = 3b
 and six years older than the other sister.
a = c+6
 If one of my sisters is half the age of the other sister,
b = .5c
 how old am I?
;
From the first two equations; a = a, therefore
3b = c+6
replace b with .5c
3(.5c) = c + 6
1.5c = c + 6
1.5c - c = 6
.5c = 6
c = 12
then 
a = 12 + 6
a = 18 yrs old 
:
:
Check this by finding the age of the other sister
b = .5(12)
b = 6
and
a = 3(6) = 18