A jogger desires to run a certain course in 1/4 less time than she usually takes. By what percent must she increase her average running speed to accomplish this goal?

(A) 20%

(B) 25%

(C) 33 1/3%

(D) 50%

(E) 75%
_________________

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?
Extra-hard Quant Tests with Brilliant Analytics

We can find answer quickly by plugging values

Lets say the course is 6 miles and she usually completes the course in 60 Minutes. Now she wants to complete the course in 1/4 less than 60 minutes which is in 45 minutes.

Now if the 6 mile course needs to completed in 1 hour, then the speed needs to be 8 Miles / hour, which is 33.5 % more than original speed.

Ans: C
_________________

Please give kudos if it helps

Resources
Ultimate GMAT Quantitative Megathread | ALL YOU NEED FOR QUANT ! ! ! | SC Blogs by Magoosh | How to improve your verbal score | Things i wish i could've done earlier | Ultimate Q51 Guide

Hello Bunuel,


I did it with a different approach but not really sure if it is the proper way to resolve this type of PS. The answer was very close to the one in the answer options. Please let me know what I did wrong.

Let's give some values to the initial time, speed, and distance that she usually takes.

D=S x T 10 =10mph x 60 min. finding S. we have S = D/T therefore S = 10/60min S1= 1/6

Now let use the information given in the argument, however, S and D are the same values. Here the time is 1/4 less than she usually takes. So T = 60 - (60 * 1/4) = 45

D = S X T 10 =10mph x 45 min. we need to find The average speed. So S = D/T therefore S = 10/45min S2= 2/9

Now we have S1=1/6 and S2=2/9.

S1---100%
S2--- X

let's find X: X = (2/9 1/6) X 100 Solution: X = 133.33% Then 133.33% - 100 % = 33.33%