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Register now and save up to $200 Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code ## OG 13 30 This topic has 2 expert replies and 0 member replies oquiella Master | Next Rank: 500 Posts Joined 12 May 2015 Posted: 164 messages Thanked: 3 times #### OG 13 30 Thu Dec 24, 2015 9:37 am Elapsed Time: 00:00 • Lap #[LAPCOUNT] ([LAPTIME]) The only gift certificates that a certain store sold yesterday were worth either$100 each or $10 each. If the store sold a total of 20 gift certificates yesterday. how many gift certificates worth$10 each did the store sell yesterday?

1. The gift certificates sold by the store yesterday were worth a total of between $1650 and$1800.
2. Yesterday the store sold more than 15 gift certificates worth $100 each. Answer: A Please explain why A is sufficient when there could have been a range between$1650 and $1800. Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums! ### GMAT/MBA Expert DavidG@VeritasPrep Legendary Member Joined 14 Jan 2015 Posted: 2301 messages Followed by: 115 members Thanked: 1069 times GMAT Score: 770 Fri Dec 25, 2015 6:57 am oquiella wrote: The only gift certificates that a certain store sold yesterday were worth either$100 each or $10 each. If the store sold a total of 20 gift certificates yesterday. how many gift certificates worth$10 each did the store sell yesterday?

1. The gift certificates sold by the store yesterday were worth a total of between $1650 and$1800.
2. Yesterday the store sold more than 15 gift certificates worth $100 each. Answer: A Please explain why A is sufficient when there could have been a range between$1650 and $1800. The key here is to recognize that we have a total of 20 gift certificates and that the number of gift certificates of each type must be an integer value. Say the store sold 17 of$100 certificates and 3 of the $10. That would give us 17*100 + 3*10 = 1730. That's between 1650 and 1800, so that's one possible scenario. Now let's see if anything else can work. What if there were 18 of the$100 certificates and 2 of the $10? That gives us a total of 1820 -not between 1650 and 1820 so this not a possibility that satisfies the statement. What if there were 16 of the$100 certificates and 4 of the $10? That gives us a total of 1640 - not between 1650 and 1800, so we can't use this scenario either. The only possibility that satisfies the statement is that there were 17 of the$100 certificates and 3 of the $10 certificates. So the answer is A _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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DavidG@VeritasPrep Legendary Member
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Fri Dec 25, 2015 7:04 am
oquiella wrote:
The only gift certificates that a certain store sold yesterday were worth either $100 each or$10 each. If the store sold a total of 20 gift certificates yesterday. how many gift certificates worth $10 each did the store sell yesterday? 1. The gift certificates sold by the store yesterday were worth a total of between$1650 and $1800. 2. Yesterday the store sold more than 15 gift certificates worth$100 each.

Please explain why A is sufficient when there could have been a range between $1650 and$1800.
Algebraically, we can say that 'x' is the number of $10 certificates and '20-x' is the number of$100 certificates. (Because we know there are 20 total.) We know that 10x + 100(20-x) is the total value of the certificates. 10x + 100(20-x) = 10x + 2000 - 100x = 2000 - 90x. We know this value is between 1650 and 1800. Now test x's.

x = 1 --> 2000 - 90 = 1910. Nope
x = 2 --> 2000 - 180 = 1820. Nope
x=3 ---> 2000 - 270 = 1730. Satisfies!
x = 4 ---> 2000 - 360 = 1640. Nope

Only one value works, so we know that x = 3.

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