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If Fran jumps straight up off the floor and lands on her fee

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If Fran jumps straight up off the floor and lands on her fee [#permalink]

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If Fran jumps straight up off the floor and lands on her feet T seconds later, her feet will reach a maximum height of 1.22T^2 meters above the floor. On one such jump, was Fran off the floor for less than 1 second?

(1) On her jump Fran’s feet reached a maximum height of 1 meter above the floor

(2) On her jump Fran spent more than 1/4 second ascending
[Reveal] Spoiler: OA

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Re: If Fran jumps straight up off the floor and lands on her fee [#permalink]

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If Fran jumps straight up off the floor and lands on her feet T seconds later, her feet will reach a maximum height of 1.22T^2 meters above the floor. On one such jump, was Fran off the floor for less than 1 second?

(1) On her jump Fran’s feet reached a maximum height of 1 meter above the floor --> 1.22T^2 = 1 --> we can find T and answer whether it's less than 1. Sufficient.

(2) On her jump Fran spent more than 1/4 second ascending --> if she spent 1/3 second ascending, then the answer is YES but if she spent 100 seconds ascending, then the answer is NO. Not sufficient.

Answer: A.
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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

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Re: If Fran jumps straight up off the floor and lands on her fee [#permalink]

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1 - sufficient. 1.22T^2 = 1, we can solve for T and hence know if it is > 1 or
< 1

2 - insufficient. If the ascend is 1/3sec, then the total is 2/3 sec which is < 1.
If the ascend is 1 sec, then total = 2 sec which is > 1

I'd vote for A
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Re: If Fran jumps straight up off the floor and lands on her fee [#permalink]

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Re: If Fran jumps straight up off the floor and lands on her fee [#permalink]

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New post 17 Jan 2016, 21:33
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.


If Fran jumps straight up off the floor and lands on her feet T seconds later, her feet will reach a maximum height of 1.22T^2 meters above the floor. On one such jump, was Fran off the floor for less than 1 second?

(1) On her jump Fran’s feet reached a maximum height of 1 meter above the floor

(2) On her jump Fran spent more than 1/4 second ascending


Modify the original condition and the question. Since her feet will reach a maximum height of 1.22t^2 after t seconds later, you need to figure out t. So, there is 1 variable, which should match with the number of equations. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer.
For 1), you can find out value of t from 1.22t^2=1, which is sufficient.
For 2), 1/4 second was spent more. So, if it is 1.1/4 seconds, it is yes. If it is 1 second, it is no and not sufficient. Therefore, the answer is A.


-> For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
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Re: If Fran jumps straight up off the floor and lands on her fee [#permalink]

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New post 24 Apr 2017, 09:18
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If Fran jumps straight up off the floor and lands on her fee   [#permalink] 24 Apr 2017, 09:18
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