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22 Mar 2025, 00:43
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
(N/A)
Question Stats:
100% (01:09) correct
0% (00:00) wrong based on 6 sessions
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Out of 5.5 billion bacteria grown for an experiment, 1 in 75 million has a particular mutation. Approximately how many of the bacteria have the mutation?
(A) 7
(B) 73
(C) 733
(D) 7,333
(E) 73,333
(A) 7
(B) 73
(C) 733
(D) 7,333
(E) 73,333
22 Mar 2025, 08:14
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Total bacteria= 5.5*10^9
Bacteria having mutation= 1/(75*10^6)
Total bacteria having mutation= (55*10^8)/(75*10^6)
= 1100/15= 220/3=73.334
Approx 73
Answer: B
Bacteria having mutation= 1/(75*10^6)
Total bacteria having mutation= (55*10^8)/(75*10^6)
= 1100/15= 220/3=73.334
Approx 73
Answer: B
23 Mar 2025, 11:25
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OE
One good way to keep track of large numbers (especially those that won’t fit in the GRE calculator!) is to use scientific notation (or a loose version thereof—for instance, 5.5 billion in scientific notation is \(5.5 × 10^9\), but it would be equally correct for your purposes to write it as \(55 × 10^8\)).
5.5 billion = 5,500,000,000 = \(5.5 × 10^9\)
75 million = 75,000,000 = \(75 × 10^6\)
Since 1 in 75 million of the bacteria have the mutation, divide 5.5 billion by 75 million:
\(\frac{5.5*10^9}{75*10^6}\), which can also be written as \(\frac{5.5}{75}\)*\(\frac{10^9}{10^6}\).
Only \(\frac{5.5}{75}\) needs to go in the calculator, to yield 0.0733333 ... Since \(\frac{10^9}{10^6}\) is \(10^3\), move the decimal three places to the right to get 73.333 ..., or answer choice (B).
Or, write one number over the other and cancel out the same number of zeros from the top and bottom before trying to use the calculator:
Answer: B
GMAT-Club-Forum-133n62ef.png [ 150.49 KiB | Viewed 176 times ]
One good way to keep track of large numbers (especially those that won’t fit in the GRE calculator!) is to use scientific notation (or a loose version thereof—for instance, 5.5 billion in scientific notation is \(5.5 × 10^9\), but it would be equally correct for your purposes to write it as \(55 × 10^8\)).
5.5 billion = 5,500,000,000 = \(5.5 × 10^9\)
75 million = 75,000,000 = \(75 × 10^6\)
Since 1 in 75 million of the bacteria have the mutation, divide 5.5 billion by 75 million:
\(\frac{5.5*10^9}{75*10^6}\), which can also be written as \(\frac{5.5}{75}\)*\(\frac{10^9}{10^6}\).
Only \(\frac{5.5}{75}\) needs to go in the calculator, to yield 0.0733333 ... Since \(\frac{10^9}{10^6}\) is \(10^3\), move the decimal three places to the right to get 73.333 ..., or answer choice (B).
Or, write one number over the other and cancel out the same number of zeros from the top and bottom before trying to use the calculator:
Answer: B
Attachment:
GMAT-Club-Forum-133n62ef.png [ 150.49 KiB | Viewed 176 times ]
