NIMCET 2007 — Computer PYQ
NIMCET | Computer | 2007The number 1/3 can be represented with finite number of terms in base :
Choose the correct answer:
- A.
7
- B.
8
- C.
9
(Correct Answer) - D.
10
9
Explanation
The Fundamental Rule of Terminating Fractions
A simplified rational fraction qp (where gcd(p,q)=1) can be expressed as a terminating (finite) fractional expansion in a given base b if and only if all the prime factors of the denominator q are also prime factors of the base b.
Mathematically:
If q=p1e1⋅p2e2…pkek
Then for a fraction to terminate in base b, every prime factor pi must perfectly divide b:
pi∣b∀ i∈{1,2,…,k}
If the base b does not share all the prime factors of q, the fractional representation will result in an infinite recurring (repeating) sequence.
Step 1: Analyze the Given Fraction
We are given the fraction:
qp=31
Here, the denominator is q=3.
The only prime factor of the denominator is 3.
Therefore, for 31 to have a finite (terminating) representation, the base b must be a multiple of 3.
3∣b⟹b∈{3,6,9,12,15,…}
Step 2: Test the Given Options
(a) Base 7: The prime factors of 7 are {7}. Since 3 does not divide 7, the expansion is infinite recurring.
(31)7=0.2222…7
(b) Base 8: The prime factor of 8 is {2} (8=23). Since 3 does not divide 8, the expansion is infinite recurring.
(31)8=0.2525…8
(c) Base 9: The prime factor of 9 is {3} (9=32). Since the prime factor 3 divides 9 perfectly (3∣9), the expansion will be finite (terminating).
Let's calculate it:
31=93=3×9−1=(0.3)9
Since it terminates in exactly one digit, it contains a finite number of terms.
(d) Base 10: The prime factors of 10 are {2,5}. Since 3 does not divide 10, the expansion is infinite recurring.
(31)10=0.3333…10=0.3
Conclusion
The number 1/3 has a finite representation only in base 9 among the given choices.
Correct Answer: (c) 9

