OFFICIAL EXPLANATIONHi All,
We're asked for the ratio of houses with smoke alarms to houses without smoke alarms on Gleaner Street. This is a value question; since it asks us for a RATIO, there are a couple of different ways that we can answer it (we either need the exact number of each type of house OR some other way to define the relationship between those two numbers).
1) On Gleaner Street, 7/18 of the houses do not have smoke alarms.
With the information in Fact 1, we know that the total number of houses is some multiple of 18 AND that the number without smoke alarms would be an equivalent multiple of 7. This creates a pattern....
IF... there were 18 houses, 7 would NOT have a smoke alarm and the remaining 11 would... so the answer to the question would be 11:7
IF... there were 36 houses, 14 would NOT have a smoke alarm and the remaining 22 would... so the answer to the question would be 22:14 = 11:7
IF... there were 54 houses, 21 would NOT have a smoke alarm and the remaining 33 would... so the answer to the question would be 33:21 = 11:7
Etc.
The answer to the question is ALWAYS 11:7
Fact 1 is SUFFICIENT
2) There are 90 houses on Gleaner Street.
Fact 2 gives us the total number of houses, but tells us NOTHING about the number that have (or do not have) a smoke alarm.
Fact 2 is INSUFFICIENT
Final Answer:
GMAT assassins aren't born, they're made,
Rich
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