Brain Teasers
How Young?
Mr. and Mrs. Silver have three daughters.
When the youngest was born, you could multiply the middle child's age by three to get the oldest sister's age.
Nine years ago, you could add the middle child's age to the youngest child's age to get the oldest child's age.
What is the youngest that the oldest child can be now?
When the youngest was born, you could multiply the middle child's age by three to get the oldest sister's age.
Nine years ago, you could add the middle child's age to the youngest child's age to get the oldest child's age.
What is the youngest that the oldest child can be now?
Hint
You can create two equations, where the three variables are:- the age of the middle child when the youngest child was born
- the age of the oldest child when the youngest child was born
- the age of the youngest child 9 years ago.
Answer
The oldest child must presently be at least 14 years old.Ages at youngest child's birth (youngest to oldest):
0, y, z
Ages 9 years ago (or x years after the youngest child was born; youngest to oldest):
0+x, y+x, z+x
There are two restrictions:
(1) At the youngest child's birth we know that 3y=z
(2) Nine years ago, the oldest child must be the sum of her two youngest sibling's ages, so x+x+y=x+z
Simplifying the two equations, we get:
z=3y
x=2y
From there, we input the lowest possible value of y, and calculate the oldest child's present age:
z+x+9
(3y)+(2y)+9
3+2+9 = 14
Hide Hint Show Hint Hide Answer Show Answer
What Next?
View a Similar Brain Teaser...
If you become a registered user you can vote on this brain teaser, keep track of which ones you have seen, and even make your own.
Solve a Puzzle
Comments
Oh, too hard for me! I didn't even try. But good anyway!
Well I liked it!
I liked it, too. My mistake was in assuming that someone could technically be zero years old. =]
I guess I should have more clear - yongest, middle, and oldest were meant to imply different ages. And it was also meant to be assumed that ages were measured in whole years (since that's the usual measurement of age).
Nicely done i had fun doing it ^^
That was waaaaay too hard for me to solve and even after reading the answer I still didn't get it
I almost got it but I had a small miscalculation Good teaser though
Very easy, I don't see why this gets rated so difficult.
Whatever the difference between the two oldest ages will be how old the youngest is when the sum of the two youngest ages equals the oldest age. The smallest the difference can be to satisfy the first condition is 2 when they are 1 and 3. 3 + 2 + 9 = 14
Way too simple to get with just a little reasoning to use algebra.
Whatever the difference between the two oldest ages will be how old the youngest is when the sum of the two youngest ages equals the oldest age. The smallest the difference can be to satisfy the first condition is 2 when they are 1 and 3. 3 + 2 + 9 = 14
Way too simple to get with just a little reasoning to use algebra.
To post a comment, please create an account and sign in.
Follow Braingle!