Fresh and invigorated after completing her algebra homework, Mimi appeared at the living room door. She held a piece of paper covered in scribbled numbers, 'm's, 'd's, and equations.
"Dad !" she announced. "Five years from now you'll be only double my age !"
"Amazing !" Dad almost looked up from the TV, but knew she hadn't finished.
"But five years ago, you were triple my age then !"
"I suppose in another ten years we'll be the same age," Dad grunted, changing channels.
How old is Mimi ?
Answer will be provided next Thursday evening after 21:00.
Teaser Of The Day No. 179
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elcarretero
- Posts: 2940
- Joined: 06 Nov 2019 22:27
- Location: Torrevieja
Re: Teaser Of The Day No. 179
ANSWER
Mimi is 15 (and Dad is 35).
There are lots of little clues that help narrow down the options to guess.
Dad's age must have been a multiple of 6 five years ago. His age was triple Mimi's and ten years later it would be a multiple of two. So it was a multiple of both 3 and 2.
Or you could use algebra:
Let m and d represent Mimi's and Dad's ages now.
1. d-5 = 3x(m-5)
2. d+5 = 2x(m+5)
d-5 = 3m-15 ... *1*
d+5 = 2m+10 ... *2*
-10 = m-25 ... subtracting *2* from *1*
So m=15
Mimi is 15 (and Dad is 35).
There are lots of little clues that help narrow down the options to guess.
Dad's age must have been a multiple of 6 five years ago. His age was triple Mimi's and ten years later it would be a multiple of two. So it was a multiple of both 3 and 2.
Or you could use algebra:
Let m and d represent Mimi's and Dad's ages now.
1. d-5 = 3x(m-5)
2. d+5 = 2x(m+5)
d-5 = 3m-15 ... *1*
d+5 = 2m+10 ... *2*
-10 = m-25 ... subtracting *2* from *1*
So m=15
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