February 23, 2019 February 23, 2019 07:00 AM PST 09:00 AM PST Learn reading strategies that can help even nonvoracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT February 24, 2019 February 24, 2019 07:00 AM PST 09:00 AM PST Get personalized insights on how to achieve your Target Quant Score.
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 53066

On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
14 Nov 2014, 08:57
Question Stats:
83% (01:42) correct 17% (01:47) wrong based on 170 sessions
HideShow timer Statistics



Manager
Joined: 10 Sep 2014
Posts: 96

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
14 Nov 2014, 10:32
statement 1: not sufficient We still need to know either the total # of people or a value for one of the groups.
statement 2: not sufficient We don't know the relationship between #of parents and #of students/teachers
Down to answers C or E.
Combined, we can use statement 1 to find the ratio of all the groups. Both ratios we are given have students. One value for students is 5 and the other is 7 so we multiple together to get 35. For every 35 students, there will then be 15 teachers and 7 parents. Using statement 2, we know that the # of parents is less than 20. With the ratios we are given, the # of parents can be 7 or 14. So we still do not have enough information to know for sure.
Answer E!



Intern
Joined: 20 Jan 2013
Posts: 33

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
15 Nov 2014, 01:20
Statement 1: From question stem  The ratio of teachers(T) to students(S) was 3 : 7 => T/S = 3/7 From statement  The ratio of the number of students(S) to parents (P) was 5 : 1 => S/P = 5/1 => S = 5P With the help of above two statements T/5P = 3/7 => 7*T/15 =P ....... Not enough info We don't know the number of teachers. Insufficient. Hence option A & D are out. Statement 2 : The number of parents on the trip was less than 20 => P < 20 So,number of parents can be any number less than 20. 19,18,17 etc. Insufficient. Hence option B is out. By combining both the statements, we can't find number of parents. Answer, E.
_________________
_________________
KUDOS is always a good way to thank anyone. It encourages someone to post more questions and also answers.
KUDOS Please if My post helps you in anyway. Your Kudos keep me alive [/color]



Manager
Joined: 22 Sep 2012
Posts: 129
Concentration: Strategy, Technology
WE: Information Technology (Computer Software)

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
15 Nov 2014, 07:47
Statement 1 and 2 are clearly insufficient.
Combining both 1 and 2, we get
teacher : student: parents = 15:35:7
Therefore possible number of parents,which is less than 20, could either be 7 or 14.
The answer should be E)



Math Expert
Joined: 02 Sep 2009
Posts: 53066

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
17 Nov 2014, 11:01
Bunuel wrote: Tough and Tricky questions: Ratios. On a certain field trip, the ratio of teachers to students was 3 : 7. What was the number of parents on the field trip? (1) On the field trip, the ratio of the number of students to parents was 5 : 1. (2) The number of parents on the trip was less than 20. Kudos for a correct solution. Official Solution:On a certain field trip, the ratio of teachers to students was 3 : 7. What was the number of parents on the field trip?We need to determine the number of parents on a field trip. Since this problem involves three unknown quantities, we will assign each quantity a variable. The number of teachers, students, and parents will be \(t\), \(s\), and \(p\), respectively. The problem tells us that \(t : s\), the ratio of teachers to students, was 3 : 7. Statement 1 tells us that \(s : p\), the ratio of the number of students to parents, was 5 : 1. Since this ratio and the ratio in the prompt contain \(s\), the number of students, then it is possible to create a ratio using all three variables by finding the least common multiple (LCM) of the two values for \(s\). The LCM of 7 and 5 is 35; multiply both ratios so that their \(s\) term is 35. Thus, \(t : s = 3 : 7\) becomes \(t : s = 15 : 35\), and \(s : p = 5 : 1\) becomes \(s : p = 35 : 7\). Combine the ratios to get \(t : s : p = 15 : 35 : 7\). This ratio gives us the relative quantities of teachers, students, and parents. However, any numbers of students, teachers, and parents that satisfy this ratio could have gone on the field trip. The numbers of teachers, students, and parents on the trip could have been 15, 35, and 7, respectively; they could also have been 30, 70, and 14. In fact, any multiple of this ratio would satisfy this statement. Statement 1 is therefore NOT sufficient. Eliminate answer choices A and D. The correct answer choice must be B, C, or E. Statement 2 tells us that the number of parents on the field trip was less than 20. This does not allow us to identify the number of parents on the field trip; it could be anywhere between 0 or 19 and still satisfy the statement. This statement is NOT sufficient to answer the question. Eliminate answer choice B. The correct answer choice is either C or E. Taken together, the statements give us the relative amounts of all three quantities and place an upper bound on the number of parents: \(p \lt 20\). However, as we saw in looking at statement 1, the first two multiples of our ratio both call for less than 20 parents. The possible values of \(p\) are limited to 7 and 14, but there is not enough information to find a single value. Both statements together are NOT sufficient. Answer: E.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Status: My heart can feel, my brain can grasp, I'm indomitable.
Affiliations: Educator
Joined: 16 Oct 2012
Posts: 39
Location: Bangladesh
WE: Social Work (Education)

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
27 Aug 2015, 02:28
let, teacher= t, students = s, parents = p from stat1 t:s = 3: 5 = 15 : 35 s:p = 5: 1 = 35 : 7 so, t : s : p = 15 : 35 : 7 we dont know the the number of teacher or students....insufficient. from stat2 the number of parents less than 20 we dont know the ratio for the parents combinging stat 1 and 2 possible number of parents are 7 or 14.....still now inconclusive ans : A
_________________
please press "+1 Kudos" if useful



VP
Joined: 09 Mar 2018
Posts: 1002
Location: India

Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
Show Tags
26 Jan 2019, 07:20
Bunuel wrote: Tough and Tricky questions: Ratios. On a certain field trip, the ratio of teachers to students was 3 : 7. What was the number of parents on the field trip? (1) On the field trip, the ratio of the number of students to parents was 5 : 1. (2) The number of parents on the trip was less than 20. Interesting question. (1) On the field trip, the ratio of the number of students to parents was 5 : 1. Just gives the ratio, this value can be 5:1 this wont give us the definite value (2) The number of parents on the trip was less than 20. No relation between students and parents, Nothing Combine both the statements, we get a relationship among all three T/S =3:7 Multiply the ratio by 5 S/P = 5: 1 Multiply the ratio by 7 T:S:P = 15 : 35 : 7 Now since parents are less than 20, the ratio can also be T:S:P = 30 : 70 :14 We are not getting a unique value E
_________________
If you notice any discrepancy in my reasoning, please let me know. Lets improve together.
Quote which i can relate to. Many of life's failures happen with people who do not realize how close they were to success when they gave up.




Re: On a certain field trip, the ratio of teachers to students was 3 : 7.
[#permalink]
26 Jan 2019, 07:20






