The time and work problems are actually practical problems and its knowledge will bring you power of taking correct decision. For example, in our day to day life we come across problem of building a bridge or digging the well in a village. These planning for work requires proper computation.

As you won't be allowed to use the calculator, your calculations should be speedy and accurate. You can practice basic calculations as and when possible. The more you practice, the faster you can solve questions on the test day. This will give you more time to solve tougher sections with ease.

Work on a process of elimination strategy. Basically it is guessing if an answer is in certain range and eliminating wrong choices. There is nothing like being able to answer a question without actually solving it but you should avoid making random guesses

Frequently, a question will test your ability not to compute, but rather to make reasonable approximations. For example, the fact that 8 goes into 69 a little more than 8 times means that 8/69 must be slightly less than 1/8.

If you cannot calculate the answer the correct option is "Data Inadequate" or "Cannot be Determined". If you found an answer not listed in the answer option the choice would be "None of these"