Let x = number of 3BR units
Let y = number of 2BR units
x + y = 210 (from "... 210 condominiums ...")
3x + 2y = 537 (from "... total number of bedrooms in the entire complex is 537...")
Mulitply the first equation by 2 and subtract that result from the bottom equation:
3x + 2y = 537
-(2x + 2y = 420)
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x = 117 --> y = 210-117 = 93
Answer:
There are 117 3BR units and 93 2BR units.
Check:
3*117 + 2*93 = 351 + 186 = 537 (total number of BR's checks out)
117 + 93 = 210 (total number of units checks out, note we used this to find y)