Question
Out of all the 2-digit integers between 1 and 100, a 2-digit number has to be selected at random. What is the probability that the selected number is not divisible by 7?
Official answer and solution
- Official answer
- D
- From
- Official GATE 2013 answer key
Solution
Count the total number of two-digit numbers and the subset divisible by 7, then compute the complementary probability.
-
Determine total number of 2-digit integers:
The 2-digit integers between 1 and 100 are . -
Count 2-digit integers divisible by 7:
The smallest 2-digit multiple of 7 is .
The largest 2-digit multiple of 7 is . -
Count integers not divisible by 7:
-
Calculate probability:
This matches option (D).
D
The answer is the one in the official GATE answer key. The solution is this site's own explanation.
Source
- Paper
- GATE 2013 Computer Science and Information Technology (CS)
- Question
- 62 of 65, printed as GA Q.62
- Section
- General Aptitude
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