Donna is one year older than her sister, and her sister is 3 years older than their brother. If the sum of their ages is 31, how old is Donna?
B + B + 3 + B + 4 = 31
Solve for B.
D = s + 1
s = b + 3 ... b = s - 3
D + s + b = 31
s + 1 + s + s - 3 = 31
find s, then substitute back
To determine Donna's age, we can follow the given information step by step:
Let's represent Donna's sister's age as x.
Based on the given information, Donna is one year older than her sister, so her age would be (x + 1).
Further, their brother is 3 years younger than the sister, so his age would be (x - 3).
Now, we need to form an equation using the sum of their ages, which is given as 31:
(x + 1) + x + (x - 3) = 31
Simplifying the equation:
3x - 2 = 31
3x = 33
x = 11
Therefore, Donna's sister's age (x) is 11.
Donna's age would be her sister's age plus one, so Donna is 11 + 1 = 12 years old.