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(1) b less than or equal to 2 (2) b is greater than or equal to negative 8

C.

These type of questions, it is much faster if you realize the critical points of the equation. In this case, critical points are b=2 and b=-8.
From this, you know that there are three intervals that the equation must satisfy.

A interval: b<-8
B interval: -8<b<2
C interval: b>2

If you find that b fall into one of these interval, then it must be right. (1) doesn't since it falls into intervals A and B, so INSUFFICIENT. (2) doesn't either because it falls into interval B and C, INSUFFICIENT. Together, it falls into interval B. SUFFICIENT.

(1) b less than or equal to 2 (2) b is greater than or equal to negative 8

C.

These type of questions, it is much faster if you realize the critical points of the equation. In this case, critical points are b=2 and b=-8.
From this, you know that there are three intervals that the equation must satisfy.

A interval: b<-8
B interval: -8<b<2
C interval: b>2

If you find that b fall into one of these interval, then it must be right. (1) doesn't since it falls into intervals A and B, so INSUFFICIENT. (2) doesn't either because it falls into interval B and C, INSUFFICIENT. Together, it falls into interval B. SUFFICIENT.

*Additional comment: for this method to be useful, you should at least plug in a value from those interval to see if which one equals 10.

If I can only freakin add on D day..arrrgggggggh...

guys any suggestions on how to avoid such mistakes????

It happens to me too when I try to do it too fast or do it at work. I suggest writing it out step by step or get a good sleep. Or maybe it is just rainy today :D

These type of questions, it is much faster if you realize the critical points of the equation. In this case, critical points are b=2 and b=-8. From this, you know that there are three intervals that the equation must satisfy.

A interval: b<-8 B interval: -8<b<2>2

If you find that b fall into one of these interval, then it must be right. (1) doesn't since it falls into intervals A and B, so INSUFFICIENT. (2) doesn't either because it falls into interval B and C, INSUFFICIENT. Together, it falls into interval B. SUFFICIENT.

Many thanks!

I also got C on this question =( But your explanation is great, it'll be definitely a shortcut for me!