GMAT Math

jasonc wrote:I tried searching the forum but only found references to the rtd chart method etc, but no actual explanation of what it is.

(I ask because there are a few people asking questions on this forum about how to solve this or that problem using the rtd method)

the poster above me is correct: it's a chart in which the columns are labeled 'rate', 'time', and 'distance'. since the relationship (rate x time = distance) always holds, you can play tic-tac-toe with the rows; i.e., if you have any two elements of a row, you can find the third element without introducing an additional variable, either by adding (if the missing element is 'distance') or by subtracting (if the missing element is 'time' or 'rate').

this chart is not exactly a work of earth-shattering genius - it can be found in any high-school algebra textbook - but you'd be surprised by the power of a humble chart to organize your thoughts. herein lies the power of the rtd chart: if you have an empty cell in the chart, then you have something to do.
if you don't have the chart, then it's easy to stagnate if you don't see how to solve the problem right away. with the chart, though, you can easily see what you're already done and what you still have to do.

by the way, rtd charts aren't just for rate-time-distance problems, any more than baby wipes are just for babies.
the following problem types can also be solved with charts that have exactly the same form and functionality as rtd charts:
* price problems (unit price x quantity = total price)
* work problems (work rate x time = total output)
* basically any other problem that uses the idea of (x PER y) times (y) = (x)

good stuff.