Tackling percentage problems in GMAT is usually tricky. The question would almost never be what they appear as. Tackling percentage problems can be effectively handled by using ‘picking numbers’ strategy. There are many instances where ‘Picking Numbers’ is the best way to solve.
The first strategy to employ while solving such questions is to pick ‘100’ for the unspecified value, because any percent of 100 is just the number itself. For example 14% of 100 is 14, and 137.2% of 100 is 137.2.
Picking 100 as the original value also makes it that much easier to do the math. Using 100 not only makes our calculations easier, but it also simplify the task of expressing the final value as a percent of the original.
Let’s see this at work with a GMAT like Quantitative reasoning question:
If a bicyclist in motion increases his speed by 30 percent and then increases this speed by 10 percent, what percent of the original speed is the total increase in speed?

In this situation, we have a bicyclist increasing his speed by 30% and then increasing that speed by 10%. We want to know what percent of the original speed the total increase in speed represents. Since the original speed is not mentioned, we have assume a value for it. Remember, the numbers that we pick do not need to be realistic. Since we’re talking about a percentage of the original speed, 100 is the easiest number to pick.
Now, if we’re increasing the bicyclist’s speed by 30%, well 30% of 100 is 30. His new speed at this point is 130. He then increases this speed by 10%. That means he’s increasing 130 by 10%, which is going to be an additional 13. Thus, his final speed is 143.
Also we’re being asked, what percent of the original speed is the total increase in speed? Again, it’s important to note that we’re looking for the total increase, not the new speed itself. The increase in this case is 43. and to find the percent of the original speed, we have 43 divided by 100, which is 43% or answer choice (C).
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