On Friday I posted this puzzle….

Right now a mother is 21 years older than her child, but in 6 years her child will be 5 times younger than her. Where is the father?

If you haven’t tried to solve it, have a go now.  For everyone else, the answer is after the break.

.75 of a year is about 9 months, so the child is very new in the womb. As a result, the father is very close!

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

1. It would have been less confusing if the puzzle had said “Right now a mother is 21 years older than her child, but in 6 years she will be 5 times as old as her child“. The wording “5 times younger than” is ambiguous, unscientific and quasi-booliakterous.

2. Anne Elk says:

All right, I’m thick. I got the answer because of the comments and because of common sense. Can someone explain the reference to 0.75 of a year? How did we jump to that?

1. Another Elk (that's my theory, anyway) says:

You have to do the alegebra/simultaneous equations Anne, then 0.75 emerges.
Richard isn’t too good at explaining how to solve his puzzles – he tends to just give the answer.

2. Using “m” for the mother’s age and “c” for the child’s age:

m = c + 21 and m + 6 = 5 (c + 6) [given values]

substituting [c + 21] for m in the second equation gives us: c + 21 + 6 = 5c + 30

subtracting 30 and c from both sides… 27 – 30 = 5c – c

this becomes… -3 = 4c

and divide both sides by 4 results in… -3/4 = c

ie the child is 3/4 of a year before being born! (because the age is negative)

3. x = child age.
6 + 21 + x = (x + 6) * 5
27 + x = 5 x + 30
27 – 30 = -3 = 5 x – x = 4 x
x = -3/4

4. Anne Elk says:

Thank you all for the explanations. Clear as day now that I’ve seen them!

3. Eddie says:

Apparently age is negative before birth.
20.25 – (-0.75) = 21
26.25/5 = 6 + (-0.75)

4. Anonymous says:

I think some of these puzzles should definitely be phrased more precisely. There has been more than one with ambiguous or confusing wording. Also – this one is a bit daft really. Such puzzles should be sensible and accurate if people are going to spend their time and brainpower trying to solve them properly. What if this particular child was born a couple of months prematurely? Not every child has automatically gestated for 9 months. And the father may well have scarpered or died shortly after the child was conceived – etc etc. The child could even have been born through artificial insemination and the father could have been ANYWHERE nine months earlier. So let’s have accurate sensible puzzles please!! 🙂

5. Alma says:

These puzzles need to be worded more accurately – a few have been too ambiguous or confusing to really be fair. This is just daft anyway. What if the child had been born a month or two prematurely? Not every baby gestates for the full 9 months, you know. So the father could easily have run off or even died soon after conception? Or what if the baby had been born via a sperm donor? The father could be anywhere in the world by the time the baby was actually conceived . . . Let’s have more sense and accuracy if people are going to spend their time and brain cells trying to work these things out properly!!! 🙂

1. ChrisR says:

yes, I’ve had that issue with double postings before…I now use Chrome and it seems to be better!

For several of these problems there’s an obvious answer when you take the question at face value, but it’s the comments that point out the flaws or alternative answers that add to the fun. As someone has said perhaps Richard is experimenting with us…

2. Dave says:

These puzzles need to be worded more accurately – a few have been too ambiguous or confusing to really be fair. This is just daft anyway. What if the child had been born a month or two prematurely? Not every baby gestates for the full 9 months, you know. So the father could easily have run off or even died soon after conception? Or what if the baby had been born via a sperm donor? The father could be anywhere in the world by the time the baby was actually conceived . . . Let’s have more sense and accuracy if people are going to spend their time and brain cells trying to work these things out properly!!!

3. Stevie says:

I think the point about taking the puzzle at face value is very important.
Yes some will be in the womb for longer or shorter durations than nine months.
Alternatively, the father could be anywhere, having deposited his sample with the bank months before!

6. I thought the wording was quite clear. When one notices that the algebra answer comes out to be 9 months how can one not immediately smile and blush.

7. Slange Navarr says:

The wording was clear enough, I thought. Quite a spunky little puzzle. A bit of fun to start the new year off. What’s wrong with that?

1. Lazy T says:

yup, why try and spoil an algebraic joke ? even if it does infer that we all spent 9 months in negative time.

2. Alma says:

Well – nothing wrong really, I suppose. I know it’s a bit of fun but I tend to be picky about things being exact. An aggravating personality fault, I know. Maybe my New Year resolution should be to lighten up. 🙂

8. ctj says:

to answer this puzzle, one must assume (1) a fetus is a child (it isn’t), (2) pregnancy occurs during or immediately after sex (it doesn’t), and (3) a human fetus gestates for exactly nine months (it doesn’t). you also need to assume that the fetus was conceived via sex, but that’s normal.

1. Alma says:

Well yes – it wouldn’t even be an embryo yet! Here’s another person at least who’s as picky as me about being precise! 🙂

9. “As a result, the father is very close!”

That’s an odd view of the causality in human reproduction. I always thought it worked the other way round.

10. Using the exact algebra noted above I got to the point of -4c=3 and thought “I must have made a mistake somewhere”, went through it again, got to the same point and thought “Maybe ‘5 times younger than her’ means something other than what I’m thinking it means” and left it at that.

11. CAPE BRETONER says:

A child who is 9 months old is certainly not still in the womb!!! Age 1 occurs 12 months AFTER birth. This is a very contrived answer. And in any case, where the father is cannot be determined by mere age. Nor does it mean that the father and mother are even a couple. Perhaps the mother is gay, and the father is a sperm donor. Silly answer/question.

1. Pedant says:

But the ‘derived’ answer is MINUS 9 months. So your argument is invalid.

2. Slange Navarr says:

The answer is in the negative, Cape. -0.75. No one is claiming that a child at 9 months old is still in the womb.

12. Hugh Janus says:

Let’s face it, many of us did not see that coming

1. Megan T says:

The father definitely knew it was coming..

2. Slange Navarr says:

Missed your latest worthless comment, Hugh; my apologies, you tragic old drunk. You always bring a smile to my face and a tear to my eye. Bless you for trying.

13. For those wanting to know why I said on Friday that the answer had overlooked something – several objections have already been raised by others, but my specific point related to the ‘sauciness’ dimension. I was just referring to the fact that conception does not take place during copulation, but some time later. Only a minor point really, given all the other problems presented by the wording of the puzzle!

1. Pro-Life says:

I’m not sure that i agree that the ” ‘sauciness’ dimension ” constitutes a “flaw in the thinking” Mike, but 11 out of 10 for backing up your suggestions on Friday by specific comments on Monday.
Far too many people say things like “I have two answers” on Friday then keep schtum on Monday, when they realise they have made a cock-up (If you will accept such a saucy turn of phrase!)

14. Anonymous says:

Hmm. Plus or minus a few days and he could’ve been on the other side of the planet. Glad I didn’t spend to long on this one.

15. Baker's Dozen says:

What?

16. Barry Goddard says:

By making all his wording sloppy, Richard is helping protect his site against bots that trawl the internet for sites to troll. If they canot understand his post they cannot botup a plausible reply.

This means Richard would never get a job as a quiz setter down the pub, let alone on a prestigious tv show or internet channel. But he does ensure the chat is mainly with humans,

17. Jerry says:

I got the correct answer of 3/4 year quickly from the algebra and “assumed” the father would be nearby, but there are two big problems with the. #1 – Age begins at birth, not at conception. #2 – The “assumption” that the father is nearby is a naive and idealized one. The father may be an unknown sperm doner or on the battlefield in Afghanistan.

1. Megan T says:

The fact remains that this is a puzzle, and you would assume that there’d be an answer that you can look at and know immediately that it’s right because of some clever trick. If you and everyone else posting similar comments are going to be so pedantic then you’ll never enjoy any of the Friday puzzles that Richard posts. Lighten up, sugar cookie.

2. Jerry says:

I Igot the answer, and explained why. I speak for those who did not. Nuts don’t mix well with sugar cookies.

3. ctj says:

Megan T, for some of us, being pedantic is precisely how we enjoy the friday puzzles!

18. Greg23 says:

My answer was ‘In the mother’ I guess that’s ‘close’ enough. Within a few minutes.

19. Another good puzzle, but could be BETTER. Since some people don’t even get the solution, it would be helpful to have an explanation.

20. Sam Steele says:

Mr. Wiseman is a professor of psychology. It is possible that these Friday puzzles are an experiment used to generate the comments, which he studies.

21. I didn’t get it. When I did the math and ended up with a negative number, I just assumed that there was a flaw in the problem and didn’t think any more about it. Clever, in a way, I guess, but mathematically…weird. Negative ages just don’t compute for me.

22. Bill T. says:

I hate the “X times smaller” construction, but I’m more than a bit of a pedant.

23. Greg says:

My first thoughts were ‘dead’ or ‘in jail’ but couldn’t get the numbers to match. Would never have thought of a negative age but for a clue I saw in someone’s comments.