Wikipedia:Reference desk/Archives/Mathematics/2013 March 1

= March 1 =

Am I smarter than a 5th grade math textbook?
I am perfectly mortified to have to be asking this at all, but I'm really confused and have no one else to consult. My husband teaches 5th grade math, and I'm helping him out by grading some papers. One of them has the following question: "Yolanda ate 2/5 of the carrots on the plate, then her brother ate 9 of the remaining carrots. Which expression shows how to find how many total carrots there were?" It's a multiple-choice question, but none of the provided answers makes any sense. The teacher's edition gives the answer as "(2/5)c - 9," but this doesn't make sense to me. Is this answer actually correct? If so, why? If not, what IS the correct answer? — Preceding unsigned comment added by 172.3.129.135 (talk) 19:46, 1 March 2013 (UTC)


 * Should be  (2/5)c-9 = 0  ,  then c can be worked out by rearranging the formula to be 22.5 carrots.....


 * Yolanda eats (2/5) x 22.5 carrots which leaves 9 carrots for her brother to eat.


 * I agree with you its a badly written question and answer.


 * Ap-uk (talk) 22:28, 1 March 2013 (UTC)


 * The problem does not state that no carrots were left at the end. If you want an expression for the number of carrots that remain, it would be (3/5)c - 9, assuming c is the number at the beginning.  So either you copied something down incorrectly, or the textbook contains a typo. Looie496 (talk) 22:49, 1 March 2013 (UTC)
 * Yes assuming no carrots left at the end this gives 15 carrots to start but the wording implies there are several remaining.-- Gilderien Chat&#124;List of good deeds 23:22, 1 March 2013 (UTC)


 * Indeed. There's not enough information to work out the number of carrots we began with, because "9 of the remaining carrots" means there were still some left over, and we're not told how many.  If c is the starting number, then the simplest expression for the starting number is, surprise, surprise, c; and the other data is just herrings in various shades of red.   Unless we assign a value, d, to the number left over at the end.  Then d = (3c-45)/5, and c = (5d+45)/3.  But if none of these are acceptable answers, then the paper contains a typo and students should not be burdened with the responsibility for that.  --   Jack of Oz   [Talk]  01:06, 2 March 2013 (UTC)

Thanks all. Actually I came to many of the same conclusions JackofOz did, but "c" wasn't a possible answer, nor was any equation or any expression with multiple variables. (And the problem was definitely asking the students to create an expression of the state of things using numbers and mathematical symbols rather than solving for an unknown value.) After posting this I was able to get in touch with my father, who went farther in math than I did (not that it should matter for a fifth-grade problem; he's just my go-to math expert) and actually enjoys this type of problem, and he didn't know what to make of it either. I know I copied it down correctly, so the problem was with the materials - and not for the first time, either. I just threw the question out altogether and gave them a score based on eleven problems instead of twelve. And now my husband's on his way home from work and we can spend the evening griping about the wretchedness of teaching materials in the state of California. — Preceding unsigned comment added by 172.3.129.135 (talk) 01:18, 2 March 2013 (UTC)


 * They just needed to write the last sentence differently. Instead of "Which expression shows how to find how many total carrots there were ?" they should have asked "Which expression shows how many carrots remain, as a function of the original number of carrots, c ?".  Your husband can have the students correct the books, either in this class or the next, to make it a reasonable practice question. StuRat (talk) 04:10, 2 March 2013 (UTC)


 * Apart from mathematical infelicities, the language of the original question also leaves a lot to be desired. "How many total carrots" - are we to assume that some of these objects are total carrots but some are only partially carrots (crosses between carrots and hedgehogs, perhaps)?  Reminds me of Eric the Half Bee.  --   Jack of Oz   [Talk]  08:21, 2 March 2013 (UTC)


 * Yes, the expression "total carrots" makes the whole question meaningless, or at least so ambiguous that you have to guess at the meaning. Even if we interpret it way StuRat suggests, the answer should be (3/5)c - 9, not (2/5)c - 9. Gandalf61 (talk) 09:59, 2 March 2013 (UTC)


 * If the question had been "total carrots eaten" then the expression would have been "(2/5)c + 9" (where c is the original number of carrots). Was this one of the options?    D b f i r s   17:52, 2 March 2013 (UTC)


 * Not to mention that anyone eating 9 whole carrots in a sitting, on a regular basis, may very well turn orange. StuRat (talk) 17:56, 2 March 2013 (UTC)
 * I have seen that happen to someone who tried to diet by filling up on carrots. Gradually going orange from the fingers onwards.Manytexts (talk) 06:16, 6 March 2013 (UTC)