Add Rates
GMAT glossary · Playbook
Definition
Converting individual work times to rates (1/t), adding those rates, then inverting for the combined time when agents work together.
Add Rates in plain English
Reach for Add Rates when machines or people work together on one job. Clues include working together, combined rate, or pipes filling. Convert times to rates (1/t), add rates, invert for combined time. Averaging the times is the classic wrong move. Rates add; times do not. If one pipe empties while another fills, subtract the emptying rate instead of adding. Keep a common time unit before you invert. Micro-example: A finishes in 3 hours (rate 1/3), B in 6 hours (rate 1/6). Together 1/3 + 1/6 = 1/2 job per hour, so combined time = 2 hours, not the average of 3 and 6. Keep units consistent (jobs per hour, not hours per job) until the final invert, and watch for pipes that drain while others fill.
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