5 ms·
First question: > 1. Masha was seven kopecks short to buy a first reading book, and Misha lacked one kopeck. They combined their money to buy one book to share
by SeanLuke 5y ago
First question:
> 1. Masha was seven kopecks short to buy a first reading book, and Misha lacked one kopeck. They combined their money to buy one book to share, but even then they did not have enough. How much did the book cost?
My goodness, that's an impressive 5 year old.
- noisy_boy 5y agoClearly you have not seen primary school math questions in Singapore's curriculum.
- natpalmer1776 5y agoHonestly this confused me at first read through. If I'm understanding it right, the book costs 7?
- SeanLuke 5y agoI figured it did.
- LeifCarrotson 5y agoI figured the same, but that's a curious definition for "combined their money". That means that Masha has no money, and Misha has six kopecks, so they combined 0 + 6 and are still short of 7. If the price was eight kopecks, they'd have one and seven each, and would have exactly enough. If it cost nine kopecks, they'd have 2 and 8, and would have more than enough. Eventually I concluded that the price must be between 7 and 8 kopecks, however, a kopeck is a fraction of a ruble, and Google tells me the exchange rate is currently something like 76 rubles per USD, and a kopeck is 1/100th of a ruble, so a tiny fraction of a penny, which is itself nearly worthless. Wikipedia says that hyperinflation in early Soviet Russia, inflation during the cold war, the 1998 redenomination of one new RUB ruble to 1000 RUR old rubles, and subsequent inflation in Russia all combine to mean that one kopeck in the early 90s is worth about 40,000 times less than one kopeck today. Similarly, my American son is sometimes confused why Mom and Dad pay for stuff at stores with dollar bills, but also have pennies, nickels, and dimes. Morris the Moose can buy a lemon drop for a penny, why does a small pack of lemon drops cost two dollars at the store? The last time you could subdivide a kopeck in half into a denga was around the 1917 revolution, so if the book cost 7 kopecks and one denga, Masha could have one denga and Misha could have 6 kopecks and one denga, and they could combine to get 7 kopecks but not have enough. The true answer is that if Masha and Misha have been collecting old kopecks forgotten between the couch cushions in their piggybanks, they'll be better off melting the coins for scrap metal, because they're not keeping up with inflation. You can barely buy a piece of paper for a ruble, much less a kopeck. Except the dengas, if they're in good condition, they should sell those to rare coin collectors for on the order of 100,000 kopecks, which is an awfully large number for a five-year-old to be dealing with.
- scotty79 5y ago> kopeck in half into a denga was around the 1917 revolution Really? I think I had 1/4 kopek coin somewhere when I was a kid (old foreign coin). I don't think it was this old.
- AlanYx 5y agoI wonder if there's an issue in translation. How could they "combine" their money if Masha had nothing to begin with? But if we assume quantities of money can be non-integers, then the problem is underconstrained.
- karamanolev 5y agoKopeck - "It is usually the smallest denomination within a currency system." I presume they used kopecks for a purpose and not rubles, dollars or another unit that can be subdivided. That forces the integerness of the amounts and thus the presence of a solution.
- Arnavion 5y agoThe solution to the second question requires half-kopeks.
- karamanolev 5y agoI looked at that problem after posting my original and was utterly confused. Would you trust yourself with an answer involving half-pennies? Seems like an error. As others pointed out, in #1, unless the kopecks are integer, the answer is underconstrained. #2 requires non-integer kopecks.
- deleted 5y ago[deleted]
- deleted 5y ago[deleted]
- watertom 5y agoThe problem is that the girls can't afford to buy a book singularly. Masha needs 7 kopecks to buy 1 book "Misha lacked one", which means to me as an native English speaker that Misha needed just one more Kopeck in order to purchase 1 book. When it's revealed that when they pool their money that they don't have enough to purchase just 1 book, I realized that the translation is faulty and stopped looking at the rest of the problems.
- bla3 5y agoHint: It's much easier if you don't know linear algebra.
- skyde 5y agoCan someone help me with this question. I tried wolframalpha but the question seem to make no sense. https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3D+x%2B7%2Cy%3Dz%2B1%2C+y%3Ex%2Bz%2C+x%3E0%2C+z%3E0%2C+y%3E0%5D https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3...
- skyde 5y agoGot it: cost is 7 https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3D+x%2B7%2Cy%3Dz%2B1%2C+y%3Ex%2Bz%2C+x%3E%3D0%2C+z%3E%3D0%2C+y%3E%3D0%5D https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3...
- corpMaverick 5y agoPlease don't spoil it for the rest of us. @dang
- Arnavion 5y agoKnowing the answer is 7 isn't a spoiler. The point is to work it out. You'd have to click the URL and see the WA input to be spoiled about that.
- 09asdf0asdf 5y agoYou can constrain the result to whole numbers by adding "y mod 1 = 0" as an additional constraint. https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3D+x%2B7%2Cy%3Dz%2B1%2C+y%3Ex%2Bz%2C+x%3E%3D0%2C+z%3E%3D0%2C+y%3E%3D0%2C+y+mod+1+%3D+0%5D https://www.wolframalpha.com/input/?i=solve+for+y%2C+%5By+%3...
- waynesonfire 5y agoneat trick, thanks.
- valbaca 5y agoYeah, this was confusing b/c to "be short" does imply that you have some money, otherwise you're 100% short of buying anything!