Hi All,

We're told that the temperature of a place at noon on a certain day is 25% higher than the temperature of the same place at midnight on the same day. We're asked for the temperature of the place at midnight. This question can be solved in a couple of different ways, but it's actually based on a 'math truism' (and knowing that truism can save you some time.

1) The temperature of the place at midnight is 20% lower than the temperature of the same place at noon.

The information in Fact 1 is the 'truism' that I mentioned earlier. If one number is 25% greater than a second number, then that second number is 20% less than the first. For example, consider the numbers 100 and 125..
125 = 25 more than 100 = 25/100 = 25% greater
100 = 25 less than 125 = 25/125 = 20% less

This is NOT 'new information'; it means the same as what the prompt gave us. As long as the temperature at noon is 25% higher than the temperature at midnight, then that measure is a possible answer to this question (for example, 4 and 5, 8 and 10, 12 and 15, etc.
Fact 1 is INSUFFICIENT

2) The temperature of the place at noon is 10 units greater than the temperature of the place at midnight.

The information in Fact 2 gives us a second unique equation, so we can set up a 'system' of equations. If X = the temperature at noon and Y = the temperature at midnight....
X = 1.25Y
X = Y + 10
With this 2 variable 'system', we can solve for Y (and there would be just one solution, so we don't actually have to do the math). If you did solve it though, you would end up with X=50 and Y=40
Fact 2 is SUFFICIENT

Final Answer: B

GMAT assassins aren't born, they're made,
Rich