Coffee and dessert

gmattester · Posted: Thu Aug 28, 2008 1:09 pm Post subject: Coffee and dessert

In a restaurant, 75% of the customers ordered dessert, what percent of the customers ordered coffee?
(1) 93% of the customers who ordered dessert also ordered coffee.
(2) 80% of the customers who ordered coffee also ordered dessert.

Can someone explain how to solve this question by making table and also with Venn diagram

leugene · Posted: Thu Aug 28, 2008 2:17 pm Post subject:

The answer should be C.

I don't know how to use type to draw a Venn, but I can try to explain. Please keep in mind that these questions have multiple possibilities. There are: 'Coffee Only', 'Dessert Only', 'Coffee and Dessert', and 'Neither'. Also keep in mind that you don't have to solve the problem, just need to know if you CAN or not.

So from statement 1, we know who ordered 'Coffee and Dessert' (93% of 75%), but we don't know who make up 'Coffee Only'. The point is to find out both 'Coffee and Dessert' and 'Coffee Only' to know who ordered Coffee in general. Therefore, A and D will not work. However, at this point we know that 'Coffee and Dessert' is a certain number [(93%of75%)=(69.75%OfAllCustomers)] (although you don't need to know that, as long as you know you COULD have found out if you tried).

Statement 2 is like 1; we find out nothing that can solve the problem on its own. However, using both, we can find out how many ordered 'Coffee Only' because we know 'Coffee and Dessert' already (69.75%), and 'Coffee Only' is 20% of all Coffee Orders. Technically, if you divided 69.75 by 0.8, you would get your answer (87.1875%OrderedCoffee, but once again, we don't need the answer as long as we know that we COULD get it if we tried.. Or had a calculator.. Which I used.. And couldn't bring myself to lie about).

I just read this over, and it is a little confusing, but I hope it helps. It's really important to not try to solve these, but I put the concrete numbers there so you believe me when I say you can find out the answers if you wanted to.

gmattester · Posted: Thu Aug 28, 2008 3:35 pm Post subject:

I tried but couldn't understand.......
Can someone explain this...

ankur_arora · Posted: Thu Aug 28, 2008 9:14 pm Post subject:

Looking at the question in the first place - it is not given that people who came to restaurant had only to choose among these two things or both or none. So i would choose option E..(Anybody comment on this )

however, if you need to solve this , it goes as follows

To answer this question we need the following information:
(total is 100%)
A-people who had coffee
B-people who had desserts
C-people who had both
D-people who had none

100=A+B-C+D
-the same eqution can be represented using a venn diag too.

question gives B and we need to find A so we need C and D

1) 93% of 75 % gives us C ie 69.75%
no information is given for solving for D so, Insufficient

2) insufficient as we dont have the % of customers who ordered coffee.

now, using both 1 and 2 to try getting the solution
80% people oredering for coffee(A) also order for dessert.
means, 80% of A=69.75% which we can solve to get A....

hence IMO C

jeffxujian · Posted: Fri Aug 29, 2008 1:39 am Post subject:

Same answer C thru a table

I plug in 100 for total number of customers, therefore,75 ppl ordered dessert and 25 did not. the table as follows:

Dessert No-desset Total
coffee .93*75/.8X X
No-coffee 100-X
Total 75 25 100

1. only give us the number of ppl who ordered both dessert and coffee, but did not give the number of ppl who ordered coffee but not dessert. Thus, insufficient.

2. we only know that .8X ppl ordered both coffee and dessert, insufficient

1+2, we have a equation .93*75=.8x, sufficient to get the value of X. So C

California4jx · Posted: Fri Aug 29, 2008 2:02 pm Post subject:

@gmattester

whats OA ? - IMO:B

look at attachment explanation