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Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once?
I would say it is a tricky question since it is ambiguous. There are 2 sources of confusion: 1) Do we count chicken, prawn, beef, and chicken, beef, prawn as same or as a different way of serving? I guess we can conclude that in one way, so we will need divide by 3! 2) Do we serve a sauce on the entree? Can we order a garlic chicken and chili beef? So we need to multiply by 8? can we order chicken without sauce? We will need to multiply by 27. Do we get a sauce in Panda Express way, we will need to multiply by 2, 3 or 4 depends on whether we can reject both or take both.
Anyway, with all this in mind, we can calculate that we have 5*4*3=60/3! = 10 * 8 = 80 Since answer C But if you will calculate an ordered permutation 60 and multiply by 2 Panda Express style, you will get incorrect 120
1> I first tried to answer assuming ordered permutation way and got 120. 2> If it is not ordered but rather a combination of 3 items (out of chicken/beef/prawn/veg/tofu) in one entry, then their should be 5C3 ways of combining them - 10 ways which then should be multiplied by 2 ways of adding sauce. So the answer was 20.
Can someone please clearly lay down the strategy if there are subtle nuances in the question?
Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once? Answer Options: -
A. 10 B. 60 C. 80 D. 100 E. 120
Take the task of creating a meal and break it into stages.
Stage 1: Select 3 entrees Since the order in which we select the entrees does not matter, we can use combinations. We can select 3 entrees from 5 entrees in 5C3 ways (10 ways) So, we can complete stage 1 in 10 ways
If anyone is interested, we have a video (below) on calculating combinations (like 5C3) in your head
ASIDE: We now have our 3 entrees, but we don't have a sauce for each entree.
Stage 2: Choose a sauce for one of of the entrees We have 2 choices (garlic or chili sauce), so we can complete stage 2 in 2 ways
Stage 3: Choose a sauce for another entree We have 2 choices (garlic or chili sauce), so we can complete stage 3 in 2 ways
Stage 4: Choose a sauce for the last remaining entree We have 2 choices (garlic or chili sauce), so we can complete stage 4 in 2 ways
By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus create a meal) in (10)(2)(2)(2) ways (= 80 ways)
Answer: C
Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.
RELATED VIDEOS
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Brent Hanneson – GMATPrepNow.com Sign up for our freeQuestion of the Dayemails
Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once? Answer Options: -
A. 10 B. 60 C. 80 D. 100 E. 120
Take the task of creating a meal and break it into stages.
Stage 1: Select 3 entrees Since the order in which we select the entrees does not matter, we can use combinations. We can select 3 entrees from 5 entrees in 5C3 ways (10 ways) So, we can complete stage 1 in 10 ways
If anyone is interested, we have a video (below) on calculating combinations (like 5C3) in your head
ASIDE: We now have our 3 entrees, but we don't have a sauce for each entree.
Stage 2: Choose a sauce for one of of the entrees We have 2 choices (garlic or chili sauce), so we can complete stage 2 in 2 ways
Stage 3: Choose a sauce for another entree We have 2 choices (garlic or chili sauce), so we can complete stage 3 in 2 ways
Stage 4: Choose a sauce for the last remaining entree We have 2 choices (garlic or chili sauce), so we can complete stage 4 in 2 ways
By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus create a meal) in (10)(2)(2)(2) ways (= 80 ways)
Answer: C
Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.
RELATED VIDEOS
Why do you have so many stages? Why wouldn't it be just two stages? I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2. Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2).
Can you explain why both of these solutions are wrong?
I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2. Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2). Can you explain why both of these solutions are wrong?
What do your values stand for?
While my solution might LOOK longer than it needs to be, I don't write out every stage on my notepad. HOWEVER, I make it very clear to myself what each is occurring at each stage. So, for example, in your 2-stage solution, 5C3 * 2, what does 5C3 represent and what does 2 represent?
Likewise, in your other solution, 5*2 + 4*2 + 3*2, what does each part represent?
Once you start articulating what each stage represents, your solutions will improve.
Cheers, Brent
_________________
Brent Hanneson – GMATPrepNow.com Sign up for our freeQuestion of the Dayemails
I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2. Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2). Can you explain why both of these solutions are wrong?
What do your values stand for?
While my solution might LOOK longer than it needs to be, I don't write out every stage on my notepad. HOWEVER, I make it very clear to myself what each is occurring at each stage. So, for example, in your 2-stage solution, 5C3 * 2, what does 5C3 represent and what does 2 represent?
Likewise, in your other solution, 5*2 + 4*2 + 3*2, what does each part represent?
Once you start articulating what each stage represents, your solutions will improve.
Cheers, Brent
Okay, here you go... 1. Why do you have 4 stages rather than two? You have 4 stages for entree * sauce * sauce * sauce. Why? Why not two stages for Entrees and Sauces. With two stages you would do the exact same thing you did, but without the additional two stage. 5C3 (choose 3 entrees from five entrees) * 2 (sauces). 2. Why is it also not appropriate to calculate as Option 1 + Option 2 + Option 3? Option 1 = 5 entrees * 2 sauces. Option 2 = 4 entrees * 2 sauces. Option 3 = 3 entrees * 2 sauces.
1. Why do you have 4 stages rather than two? You have 4 stages for entree * sauce * sauce * sauce. Why? Why not two stages for Entrees and Sauces. With two stages you would do the exact same thing you did, but without the additional two stage. 5C3 (choose 3 entrees from five entrees) * 2 (sauces).
It would help if you actually defined each stage. For example: STAGE 1: Choose 3 entrees This stage can be completed in 5C3 (aka 10) ways
STAGE 2: What is happening here? Is it "Choose a sauce"? If so, which entree are you choosing a sauce for? Each entree must have its own accompanying sauce. So, for example, ONE outcome (aka meal) might be: chicken with chili sauce, beef with garlic sauce, and vegetable with chili sauce
RefError wrote:
Okay, here you go... 2. Why is it also not appropriate to calculate as Option 1 + Option 2 + Option 3? Option 1 = 5 entrees * 2 sauces. Option 2 = 4 entrees * 2 sauces. Option 3 = 3 entrees * 2 sauces.
This looks like you are repeating many possible meals. So, your answer will be far too big.
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Brent Hanneson – GMATPrepNow.com Sign up for our freeQuestion of the Dayemails
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36% (01:22) correct 
