Join WhatsApp Icon JEE WhatsApp Group
Question 80

An ordinary dice is rolled for a certain number of times. If the probability of getting an odd number 2 times is equal to the probability of getting an even number 3 times, then the probability of getting an odd number for odd number of times is:

We are told that a dice is rolled $$n$$ times. The probability of getting an odd number on a single roll is $$\frac{1}{2}$$ and similarly for an even number.

The probability of getting an odd number exactly $$k$$ times follows a binomial distribution: $$P(X = k) = \binom{n}{k} \left(\frac{1}{2}\right)^n$$.

We are given that the probability of getting an odd number 2 times equals the probability of getting an even number 3 times. So $$\binom{n}{2}\left(\frac{1}{2}\right)^n = \binom{n}{3}\left(\frac{1}{2}\right)^n$$.

This simplifies to $$\binom{n}{2} = \binom{n}{3}$$, that is, $$\frac{n(n-1)}{2} = \frac{n(n-1)(n-2)}{6}$$.

Dividing both sides by $$\frac{n(n-1)}{2}$$, we get $$1 = \frac{n - 2}{3}$$, so $$n = 5$$.

Now we need the probability of getting an odd number an odd number of times, i.e., $$P(X = 1) + P(X = 3) + P(X = 5)$$ with $$n = 5$$.

$$= \left(\frac{1}{2}\right)^5 \left[\binom{5}{1} + \binom{5}{3} + \binom{5}{5}\right] = \frac{1}{32}(5 + 10 + 1) = \frac{16}{32} = \frac{1}{2}$$

Hence, the correct answer is Option D.

Get AI Help

Create a FREE account and get:

  • Free JEE Mains Previous Papers PDF
  • Take JEE Mains paper tests

JEE Quant Questions | JEE Quantitative Ability

JEE DILR Questions | LRDI Questions For JEE

JEE Verbal Ability Questions | VARC Questions For JEE

Free JEE Topicwise Questions

JEE Rotational MotionJEE Units & MeasurementsJEE Atomic StructureJEE GravitationJEE Periodic Table & PeriodicityJEE StatisticsJEE Inverse Trigonometric FunctionsJEE Magnetism & Magnetic MaterialsJEE Sequences & SeriesJEE MatricesJEE Alternating CurrentsJEE Carboxylic AcidsJEE Permutations & CombinationsJEE Work, Energy & PowerJEE Electromagnetic InductionJEE Electronic DevicesJEE d and f-Block ElementsJEE Chemical KineticsJEE Heat TransferJEE Three Dimensional GeometryJEE Magnetic Effects of CurrentJEE Hydrocarbons - AromaticJEE Electromagnetic WavesJEE Aldehydes & KetonesJEE Hydrocarbons - AlkanesJEE Applications of DerivativesJEE EquilibriumJEE Indefinite IntegrationJEE Chemical ThermodynamicsJEE ElectrochemistryJEE ProbabilityJEE BiomoleculesJEE Continuity & DifferentiabilityJEE Kinetic Theory of GasesJEE Vector AlgebraJEE Hydrocarbons - AlkynesJEE Differential EquationsJEE Current & ResistanceJEE Straight LinesJEE WavesJEE Redox ReactionsJEE Hydrocarbons - AlkenesJEE DeterminantsJEE SolutionsJEE Ray OpticsJEE Dual Nature of Matter & RadiationJEE Chemical Bonding & Molecular StructureJEE Complex NumbersJEE Sets, Relations & FunctionsJEE Electric Charges & FieldsJEE Laws of MotionJEE Fluid MechanicsJEE Basic Concepts in ChemistryJEE Trigonometric FunctionsJEE LimitsJEE Laws of ThermodynamicsJEE Kinematics - 2D MotionJEE p-Block Elements (Groups 13-18)JEE Simple Harmonic MotionJEE Electric Potential & CapacitanceJEE Coordination CompoundsJEE JEE 2D GeometryJEE CirclesJEE Definite IntegrationJEE EMF & Circuit AnalysisJEE Surface TensionJEE Atoms & NucleiJEE Laboratory Experiments - XIJEE Number SystemJEE Basic Principles of Organic ChemistryJEE Wave OpticsJEE Quadratic EquationsJEE Alcohols, Phenols & EthersJEE Organic Compounds with HalogensJEE DifferentiationJEE Conic SectionsJEE Nitrogen-Containing CompoundsJEE ElasticityJEE Practical Organic ChemistryJEE Kinematics - 1D MotionJEE Purification & CharacterisationJEE Binomial Theorem
Ask AI