I wonder if they do this on purpose?

[plonq]

This Mensa calendar seems to have one bad page per month.  I enjoy the little brain exercises every day, but ones like this drive me up the wall:

Eight chocolate bars plus six gumdrops cost 70¢.  You could buy seven gumdrops for the price of two chocolate bars.  How much change will you get back from $1.00 if you buy six of each?


The answer is: What fucking planet do these guys come from?  Let's just check their math.

8c + 6g = 70¢
7g = 2c ... 3.5g = c

Okay, now let's substitute.

8(3.5g) + 6g = 70¢ ... 28g + 6g = 70¢ ... 34g = 70¢

Unless I've done something wrong, 34 gumdrops cost 70¢

That means one gumdrop = 2.0588235294117647058823529411765¢

But hang on...

7g = 2c ... g = 2/7c
8c + 6(2/7c) = 70¢ ... 8c + 12/7c = 70¢ ... 68/7c = 70¢ ... 68c = $4.90

Therefore a chocolate bar costs 7.2058823529411764705882352941176¢

If you bought 6 gumdrops and 6 chocolate bars you would get 44.411764705882352941176470588242¢ back in change.

Their expected answer:

ANSWER: 46¢ (A chocolate bar costs 7¢; a gumdrop costs 2¢.)

Hmph.  They didn't say anything about rounding to the nearest cent in the original problem.

Comments

[shockwave77598.livejournal.com]

Lessee.

8y + 6x = 70.
2y=7x, y = 7/2x
28x + 6x = 70. x=2.05882353 cents per gumdrop

each candybar = 7.20588235 cents

6 candybars = 43.2352941
6 gumdrops = 12.3529412
sum= 55.5882353

Change for a dollar = 44cents. (frac pennies are lost)

(checks answer)

Hmph! Rounding to nearest penny - they've obviously never seen a gas pump or a credit card statement...

[dakhun.livejournal.com]

You won't get any change, because any store that sells chocolate bars for only 7¢ and then rips you off by 2¢ whenever you make a 68¢ purchase is not going to be in business much longer. ;-)

You could buy seven gumdrops for the price of two chocolate bars.

Actually, to be nitpicky, this does not imply that 7g=2c, because they don't say "exactly seven", and they don't say you would have to pay the same amount, nor do they say you won't get change. They just say "you could buy ... for".
What it means is that two chocolate bars cost at least as much as what 7 gum drops costs, but presumably (though not necessarily) less than what 8 gum drops would cost.

[caveman-joe.livejournal.com]

All seems like a load of bollocks to me. At no point in my lifetime has a bar of chocolate ever cost 7p, let alone 7 cents, let alone 7.2 cents.
Their choices of values versus representations could have been a lot better.

[tzisorey.livejournal.com]

Maybe they expect you to use the take-a-penny-leave-a-penny tray?

I wanna know where they get the concept of a chocolate bar for 7¢ - I can't get them for less than $1.20 each in Australia.

[typographer.livejournal.com]

If a chocolate thingie costs 7 cents, and a gumdrop costs 2 cents, then the original relationship they tell us is wrong.

8c + 6g = 70

8(7) +6(2) = 70

56 + 12 = 70

68 /= 70

it's a bigger problem than rounding off to the nearest penny. This reminds me of that "math" calendar I get given every few years. About one in ten of it's problems has a serious error.

[patchworking.livejournal.com]

EXACTLY! That's the answer I came up with, and was scratching my head when my math didn't come out right.

Thanks :)

[shiny-puppy.livejournal.com]

Wow, that was kind of fun. I got the right answer and didn't hesitate about rounding up to the next penny. I work in retail, you always round up. I managed to do all the division and such right, but made 12+42=46. Addition defeats me.