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How many D

by sanju09 » Thu Apr 09, 2009 3:57 am
L spends total $6.00 for one kind of D and one kind of C. How many D did he buy?

(1) The price of 2 D was $0.10 less than the price of 3 C.

(2) The average price of 1 D and 1 C was $0.35.



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by kanha81 » Thu Apr 09, 2009 8:05 am
The first time I solved this problem, I got it wrong. Here's how I would attempt to solve.

Let n: number of D's sold
m: number of C's sold
d: price of 1 D
c: price of 1 C

First try:
Given, d + c = 6
i) 2d = 3c - 0.10

Here I thought it's solvable because I have 2 equations 2 variables. hence A or D

ii) Avg. price = (d+c) / 2 = 0.35
=> d + c = 0.70

Cannot solve because we have 2 equations with same quantities of D and
C.

Therefore, [A]

Second try:
Given, d + c = 6

i) 2d = 3c - 0.10
No information on total number of C's or D's sold. Only information about the price give. Hence B, C, or E

ii) d + c = 0.70
No new information besides what's given. Hence C or E

i) & ii) No information on total number of C's or D's. Nothing new. Hence [E]

Take-aways: Just by seeing 2 variables and 2 equation don't think that you can find what is asked for in the question. Understand the question FIRST.

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by vittalgmat » Thu Apr 09, 2009 9:24 am
Hi Sanju,
This looks like the Donut and cupcake problem?

Look at the discussion here
https://www.beatthegmat.com/lew-s-doughn ... 34411.html

Thanks though for for your effort to create a new problem.
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by sanju09 » Fri Apr 10, 2009 3:36 am
vittalgmat wrote:Hi Sanju,
This looks like the Donut and cupcake problem?

Look at the discussion here
https://www.beatthegmat.com/lew-s-doughn ... 34411.html

Thanks though for for your effort to create a new problem.
Not all questions that I post here are my own creations; you can take this question for instance. The plain and simple identity of my own questions is that it won’t include the OA along with the post, otherwise is not always true. I pick and post only those questions here that I personally feel must be attempted by its mass for one reason or the other.

What I shall be doing from next time and onwards, I shall be writing MBM meaning Made By Me beneath all questions that are coming straight from my own kitchen; right vittalgmat!
The mind is everything. What you think you become. -Lord Buddha



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by vittalgmat » Fri Apr 10, 2009 9:17 am
No worries my friend!!!.
I truly appreciate your attempt to create problems. Though D and C were easy to figure out.. I may not figure out others.. Such simple changes can put our thinking hats out of whack. So my request is: Keep it coming!!!.

I think MBM is a good idea, so that ppl who attempt these problems will know what they are signing up for :-).

All in good jest
-V
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