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One die has two faces marked \(1\), two faces marked \(2\), one face marked \(3\) and one face marked \(4\). Another die…

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One die has two faces marked \(1\), two faces marked \(2\), one face marked \(3\) and one face marked \(4\). Another die has one face marked \(1,\) two faces marked \(2\), two faces marked \(3\) and one face marked \(4\). The probability of getting the sum of numbers to be \(4\) or \(5\), when both the dice are thrown together, is

[JEE Main 2025, 23 Jan (Shift 1)]

a

\(\frac{1}{2}\)

b

\(\frac{3}{5}\)

c

\(\frac{2}{3}\)

d

\(\frac{4}{9}\)

✓ Correct answer: a)

\(\frac{1}{2}\)

Explanation

outcomes for one dice =\(\left{1,1,2,2,3,4\right}\)

outcomes for another dice =\(\left{1,2,2,3,3,4\right}\)

Identifying Favorable Outcomes for a Sum of \(4\):

\( (1, 3) \): Probability = \(\frac{1}{3}\times \frac{1}{3}=\frac{1}{9}\)

\( (2, 2) \): Probability \(=\frac{1}{3}\times \frac{1}{3}=\frac{1}{9}\)

\( (3, 1) \): Probability \(=\frac{1}{6}\times \frac{1}{6}=\frac{1}{36}\)

Identifying Favorable Outcomes for a Sum of \(5\):

\( (1, 4) \): Probability \(=\frac{1}{3}\times \frac{1}{6}=\frac{1}{18}\)

\( (2, 3) \): Probability \(=\frac{1}{3}\times \frac{1}{3}=\frac{1}{9}\)

\( (3, 2) \): Probability \(=\frac{1}{6}\times \frac{1}{3}=\frac{1}{18}\)

\( (4, 1) \): Probability \(=\frac{1}{6}\times \frac{1}{6}=\frac{1}{36}\)

Calculating the Total Probability:

\(P(\text{Sum}=4\text{or}\text{Sum}=5)=P(\text{Sum}=4)+P(\text{Sum}=5)\)

\(=\left(\frac{1}{9}+\frac{1}{9}+\frac{1}{36}\right)+\left(\frac{1}{18}+\frac{1}{9}+\frac{1}{18}+\frac{1}{36}\right)\)
\(=\frac{1}{2}\)

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