[QR] question

[299678]

a reduction of $2 per kg enable a man to purchase 4 kg more rice for $240. FInd the original price of rice per kg
a) $24 b) 20 c) 12 d) 14 e) 4

I need your brief explanation for this question. solution manuals
if original price = x

240/x +4 = 240/(x-2) and correct answer is 12

I did [240/(x-2)] + 4 = 240/x

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[casper22]

I think there are some problems that are easy if you solve them backwards, and this is one of them...

my approach to such problem is to look at the answer choice and start from something that is in the middle, in most cases, that answer choice will be choice c.. however, here it is choice d, 14, I have 2 numbers above and below this number, so based on the 1st calculation and thats not the answer, you can get an idea which way u want to move with the next choice...

from there do a quick and dirty method, if initial price is 14, then for $240 he would get 240/14 units of rice, now $2 is reduced, he would get 240/12 unit, if this is 4 more than 240/14, the answer is 14, if not do the same for next answer choice...

 

[Pat Kelly]

I think there are some problems that are easy if you solve them backwards, and this is one of them...

my approach to such problem is to look at the answer choice and start from something that is in the middle, in most cases, that answer choice will be choice c.. however, here it is choice d, 14, I have 2 numbers above and below this number, so based on the 1st calculation and thats not the answer, you can get an idea which way u want to move with the next choice...

from there do a quick and dirty method, if initial price is 14, then for $240 he would get 240/14 units of rice, now $2 is reduced, he would get 240/12 unit, if this is 4 more than 240/14, the answer is 14, if not do the same for next answer choice...

that takes way too much time to do, you only have 45 mins for 40 questions, you can't blow it all on word questions that you plug and chug. You either get the algebraic equation or you guess and move on. I mean if you think about it, you already have the algebraic equation solved anyways when you try it with 14 - so you can either get it right in one try or potentially waste 2-3 tries to get the right answer. plug and chug only works if you know the algebraic expression, so if you know it you might as well solve for the right answer.

For the OP - 240/(x-2) should be larger than 240/x, right? and the problem states that 240/(x-2) is 4 more than 240/x, so 240/(x-2) = 240/x + 4. To think of it another way, 240/x is the original amount of rice, and at the new price (x-2), the new amount of rice - 240/(x-2), should be 4 more, so 240/(x-2) = 240/x + 4.

 

[DQLEUCD]

a reduction of $2 per kg enable a man to purchase 4 kg more rice for $240. FInd the original price of rice per kg
a) $24 b) 20 c) 12 d) 14 e) 4

I need your brief explanation for this question. solution manuals
if original price = x

240/x +4 = 240/(x-2) and correct answer is 12

I did [240/(x-2)] + 4 = 240/x

A x B = 240

(A-2)(B+4)=240 solve for A

AB -2B +4A -8

[(A)(240/A) - 2(240/A) +4A - 8] x A =

240A -480 + 4A^2 - 8A

[4A^2 + 232A - 480] / 4 =

A^2 + 58A - 120 = 0 and solve

[-b +/- (b^2 - 4ac)^1/2] / 2a and solve