GMAT Strategy

I have listed couple of questions below to give you some idea of what exactly I am about to talk.

Find the number of selections that can be made taking 4 letters from the word"ENTRANCE".


In the above word , the number of arrangements using the 4 letters


Tom, Jerry, and Donald and other three people sit in a line. From left to right, if Tom cannot sit on the first seat, Jerry cannot sit on the second seat, and Donald cannot sit on the fourth seat, hoe many different arrangements are possible?

These problems are not difficult at all. In fact I have answered all these problems on the problem solving forum. These problems are not only tedious but also "brain consuming".

I would like to know if problems of such kind can appear on the actual GMAT? If yes then in what score range would you classify such problems.

I don't come from a heavy math background, but I can say I am good at GMAT quant since I am scoring in higher 40's but on the actual GMAT I want to score at least 51.

Any suggestions, strategy or insight is highly appreciated.

Thanks