Please do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

A man spends a fifth of what is in his wallet, and then one fifth of what remained. He has spent a total of £72. What was the amount originally in his wallet?

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.

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20 seconds. No calculator needed.

Took me about a minute. A satisfying answer which I know is right – I’ve struggled in past few weeks!

A straight arithmetic problem with easy numbers no less. <30secs.

Easy one, less than 1 minute

Yep – few minutes

I’m not as clever as the other dudes who post on this site so it has taken me many hours to find an answer that I am still not fully confident with.

Your honesty made my day – I often feel the same with the most puzzles 😉 !

SPOILER ALERT!!!! DO NOT READ THIS IF YOU DON’T ALREADY HAVE AN ANSWER.

one fifth of one fifth is one twenty-fifth. one twenty-fifth plus one fifth is six twenty-fifths. seventy-two equals six twenty-fifths. six multiplied by four equals twenty-four. seventy-two multiplied by four equals two-hundred eighty eight. seventy-two divided by six equals twelve. two-hundred eighty eight plus twelve equals three hundred dollars. thirty seconds, no calculator, I am eight years old.

Anonymous …

1) don’t be an idiot and post the answer, it clearly says not to

2) don’t be a double idiot by posting the wrong answer

About 2 minutes no calculator just good ole fashioned brain power 🙂

it’s ok

Yeah, less than a minute I think, including a little chat with myself to have a go. Used a calculator though…

Something of a mugger’s wet dream given the amount of cash he was carrying.

Good point. Other than professional (or amateur) gamblers, who would carry around THAT much cash with them?

I got caught out at first my misreading the question but I’m happy with the answer.

I seem to have found the answer in less than 2 minutes… However, is there catch?

Around 1 minute – got a surprise with the simple figures though !

You Brits are fast! it took me 5 minutes with a calculator and just plugged and chugged until I get it. American math system blows. Looking forward to the algebraic solution

I’m surprised. I haven’t heard about plugging and chugging for a while. very reliable, though.

About 45 seconds.

<30 sec in my head after reading the problem. the wording is confusing…took me longer to read the darn problem than solving it…

straight math, easy numbers.. looks like this was for an ego boost. Bracing myself for next week.

Harish P? I know a Harish at my school.

Am Harish Jayagopal, that must b someone else.

5 sec of real thinking.

Liked the puzzle. I wish I could write puzzles like this.

Hazarded a guess, and the maths showed I got it right first time.

Nice one. About a minute or so to solve.

Easy peasy, but love the maths ones 🙂

About 30 seconds.

It boils down to an equation. I’m surprised that people got it without using pen and paper.

Played on a whiteboard, assuming £100 to start so the fractions would be easy. Then realised what the real answer would be. Now I just need to figure out how I could have done it with just brain power alone.

I can NEVER do these without a pen and paper! I don’t know where I’d even start if I only had a calculator…

Working it in reverse order, with just a tiny bit of initial logic, and it’s quite simple to do in your head.

It’s a good one. Went wrong the first time and concluded that he had less money to begin with than he ended up with. Then I realised the error. Two minutes – with good old-fashioned algebra.

About 5 minutes. Had to use a bit of algebra. I’m not as sharp as when I was was much younger.

Weird. Instinctively thought of an answer as I read it and it turned out to be correct.

Evidently I’ve spent too long thinking about higher rate pension contributions with the 20% grossing up followed by the 20% PTR rebate.

I bet you say that to all the girls, Dave – what an awesome chat up line.

Boring!

wow – even a thicko like me got that in about 10 seconds 🙂

5y=4x

x+y=72

5x = initial value;

i think this is it.

i am confused by phrase “and then one fifth of what remained” does this mean one fifth remained in his wallet? so he spend fourth fifths?

At first I thought this would be a tricky maths question that I’d need a calculator for.

Then I made an estimated guess in about 5 seconds, and rationalised that the first ‘one fifth’ would have to be exactly one fifth more than the second ‘one fifth’.

Subsequent calculations revealed my guess to be correct!

I ‘ready reckoned’ the answer in seconds then wasted about 10 mins filing the back of an envelope with gibberish.

Got it. 1 min of simple math. I hope I’m right.

Just chugged in some numbers, until I got it nicely to 72

I think I worked it out, I just picked a nice, round number to start with and found I only had to double it! That took about a minute.

For once I used Maths instead of trial and error. Took about 3 minutes, but then I’m not very good at Maths.

Several minutes using algebra, with my fuzzy “just woke up” head on.

A few minutes using simple algebra, I’m still trying to think of a neater solution though.

He would have spent £200 even. 200/ 5= 40 40- 200= 160 160/ 5= 32 40+ 32= 72 Thanks

– Evan Cohrs

Brilliant, genius. I’m sure you know how to tie your shoelaces as well, although I’m not sure I’d trust you to sit the rght way round on the toilet. Unfortunately you didn’t know how to read the bit about not giving the answer away.

Same here. I tried it out with several values. I was sure thats a even number. But how is the correct formula ? What if the spent were 194654 Pounds ? Haha ?

By the way: “Please do NOT post your answer,…solution on monday”

This puzzle is lame, anyone with grade 9 algebra could solve it, I agree, the question takes longer to read than solve! Straight Algebra….where’s the puzzle?

I’ve worked out that if he did this iteration 45 times he’d have less than a penny remaining.

Got it – initial attempt at solving the Friday quiz … about 1 minute

Got it, after reading all the hints and frigging with numbers for long enough. Still no clue what the formula should be. I probably shouldn’t be in university.

Took a minute to find a scrap of paper, a minute to write equations, then a minute to solve.

Less seconds than the answer in £…

Next one please

About a minute

That was an easy one… I spent a total of 72 seconds to solve it 🙂

Too easy.

I’ve given this to my math students at school. Just think clearly and write down what you think.

I seem to remember there is a proper method for figuring these things out, but not being able to remember it I resorted to heuristics. Managed to get it in a minute or so.

I took just too much time as compared to all the others 😦

first tried with equations and got wierd results, then with a random number and got the correct value (by chance) and then went back to the equations and got it,…

I am sure on Monday we ll see a different way of resolving it with much less paper and pencil….

about 5 min, used my phone tho, as paper, could have done it faster if I had actual paper:) no calculator tho.

It took 5 minutes tops… Im pretty sure I have it right

For the first time in ages I have got it quickly.

2 Minutes, inclusive finding something to draw on…

About 10 seconds.

Ten seconds. 🙂

About 1 or 1-1/2 minutes using a calculator since one was right at my elbow. Probably could have just as easily done it using algebra and mental calculations.

I guessed what number it would be instantly. But wrote the algebra out and solved for x just for good measure 🙂

I love algebra! But this was pretty easy–less than a minute. And I want to trade him wallets. 🙂

simple arithmetic, nice for a change. 10-15 secs

I’ve been reading this blog for your excellent when. Keep up the brilliant job you are doing here.