At the recent inter-departmental jam making contest, four lucky candidates took part to make the juiciest strawberry jam. The ages of the contestants were 14, 17, 20 and 22. As it happens the person who came last was the oldest, whereas Stuart was three years older than the person who came second. James was neither the oldest nor the youngest and Kev finished ahead of the 17 year old, but didn’t win. John was also unlucky this time and didn’t win either. Can you determine who finished where and how old they are? (Source: A Daily Brain Teaser)
This sets up nicely for a process of elimination. We’ll begin with a table of all possibilities and then remove items based on knoweledge gained (i.e. logical deduction).
|
14 |
17 |
20 |
22 |
| first |
J Ja K S |
J Ja K S |
J Ja K S |
J Ja K S |
| second |
J Ja K S |
J Ja K S |
J Ja K S |
J Ja K S |
| third |
J Ja K S |
J Ja K S |
J Ja K S |
J Ja K S |
| last |
J Ja K S |
J Ja K S |
J Ja K S |
J Ja K S |
To begin, we know that the oldest person ended up in last, so we can eliminate all from (1,4),(2,4),(3,4),(4,1),(4,2),(4,3)
|
14 |
17 |
20 |
22 |
| first |
J Ja K S |
J Ja K S |
J Ja K S |
|
| second |
J Ja K S |
J Ja K S |
J Ja K S |
|
| third |
J Ja K S |
J Ja K S |
J Ja K S |
|
| last |
|
|
|
J Ja K S |
Furthermore, we know that Kevin did not win (eliminating him from (1,1),(1,2),(1,3)), but also that he placed higher than the 17 year old. Since we know the 17 year old did not place last, then he (the 17 year old) must have placed at least third, meaning Kevin must have placed second (eliminting him from (3,1),(3,2),(3,3),(4,4))
|
14 |
17 |
20 |
22 |
| first |
J Ja S |
J Ja S |
J Ja S |
|
| second |
J Ja K S |
J Ja K S |
J Ja K S |
|
| third |
J Ja S |
J Ja S |
J Ja S |
|
| last |
|
|
|
J Ja S |
Now, we’ll knock off four at once here. First, we know James is neither the oldest nor the youngest so he can be eliminated from (1,1),(2,1),(3,1),(4,4). We also know that Stuart is three years older than the second place contestant. Since only the 17 year old and 20 year old are three years older than another contestent, Stuart must also not be the oldest or youngest so he too can be eliminated from (1,1),(2,1),(3,1),(4,4). Now, you’ll notice only John remains in (4,4) so clearly he is the 20 year old who finished in last and can thusly be eliminated from the rest of the table. Notice also that we have proved that James and Stuart must be the middle aged persons so Keven must be 14.
|
14 |
17 |
20 |
22 |
| first |
|
Ja S |
Ja S |
|
| second |
Kevin |
Ja S |
Ja S |
|
| third |
|
Ja S |
Ja S |
|
| last |
|
|
|
John |
Finally, since we know Stuart is three years older than the second place contestant, and Kevin finished second, Stuart must be 17, leaving only James for the 20 year old. To complete the solution, we know that Kevin finished higher than the 17 year old, so Stuart must have finished third, leaving James as the first place contestant.
|
14 |
17 |
20 |
22 |
| first |
|
|
James |
|
| second |
Kevin |
|
|
|
| third |
|
Stuart |
|
|
| last |
|
|
|
John |