Sets for an overlapping sets problem it is best to use a double set matrix to organize the information and solve. Fill in the information in the order in which it is given

Let's first analyze Statement (1) alone: Greg's average speed is  that of Brian's.
This indicates that Brian is traveling 1.5 times faster than Greg. If Greg's rate is r, than Brian's rate is 1.5r. However, recall that Brian also has a greater distance to travel.
To determine who will arrive first, we use the distance formula: Whoever has a shorter TIME will arrive first.

Greg's time =

Brian's time =

Since Brian is traveling for less time, he will arrive first. Statement (1) alone is sufficient.
Let's now analyze Statement (2) alone: Brian's average speed is 20 miles per hour greater than Greg's.
This gives us no information about the ratio of Brain's average speed to Greg's average speed. Thus, although we know that Brian's distance is approximately 1.4 times Greg's speed, we do not know the ratio of their speeds, so we can not determine who will arrive first.
For example, if Brian travels at 25 mph, Greg travels at 5 mph. In this case Brian arrives first. However, if Brian travels at 100 mph, Greg travels at 80 mph. In this case Greg arrives first.
Therefore, Statement (2) alone is not sufficient.
Since statement (1) alone is sufficient, but statement (2) alone is not sufficient, the correct answer is A.


25.
From 1, V>16feet/second=(16/5280)/(1/3600)=10.9mile/hour, the distance that he cycled is greater than 10.9*1/2=5.45. We cannot know whether it greater than 6.
From 2, V<18feel/second=(18/5280)/(1/3600)=12.27mile/hour, the distance that he cycled is less than 12.27*1/2=6.135.
Combine 1 and 2, 5.45Answer is E.


26.
1). Insufficient, no idea about the car's speed for the next 200 kms
2) (Actual speed + 20) * (actual time - 1 hour) = 400 kms = actual speed * actual time
Can solve for actual time
Answer is B


27.
1). x/50+(530-x)/60=10, so, x can be solve out and x/50 will be the answer
2). The time cost on two distances could be 5h, 1h; 6h, 2h;... insufficient.
Answer is A


28.
When cyclist stops, the distance between he and the hiker is 20*5-4*580
So, the cyclist will wait 80/420 minutes.

29.
90/(v+3) - 90/(v-3)=0.5

v=33
So, t=90/36=2.5