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One card is drawn at random from a well shuffled deck of 52 cards. In which of the following cases are the events $\mathrm{E}$ and $\mathrm{F}$ independent?
(i) E: ‘the card drawn is a spade’ F: ‘the card drawn is an ace’
(ii) E: ‘the card drawn is black’ $\mathrm{F}$ : ‘the card drawn is a king’
(iii) E: ‘the card drawn is a king or queen’ F: ‘the card drawn is a queen or jack’.

Solution:

Given: A deck of 52 cards.

Concept: Two events are independent, statistically independent, or stochastically independent if the occurrence of one does not affect the probability of occurrence of the other.
Calculation:

(i) In a deck of 52 cards, there are 13 spades, 4 aces, and only one card that is both a spade and an ace.

Hence, $P(E)=$ the card drawn is a spade $=13 / 52=1 / 4$

$\mathrm{P}(\mathrm{F})=$ the card drawn is an ace $=4 / 52=1 / 13$

$P(E \cap F)=$ the card drawn is a spade and ace both $=1 / 52 \ldots . .$ (1)

And $P(E) . P(F)$

$=1 / 4 \times 1 / 13=1 / 52 \ldots .(2)$

From (1) and (2)

$\Rightarrow P(E \cap F)=P(E) . P(F)$

Hence, $\mathrm{E}$ and $\mathrm{F}$ are independent events.

(ii) In a deck of 52 cards, 26 cards are black, 4 cards are king, and there are only two cards that are both black and king at the same time.

Hence, $P(E)=$ the card drawn is of black $=26 / 52=1 / 2$

$P(F)=$ the card drawn is a king $=4 / 52=1 / 13$

$P(E \cap F)=$ the card drawn is a black and king both $=2 / 52=1 / 26 \ldots$ (1)

And $P(E) . P(F)$

$=1 / 2 \times 1 / 13=1 / 26 \ldots .(2)$

From (1) and (2)

$\Rightarrow P(E \cap F)=P(E) \cdot P(F)$

Hence, $\mathrm{E}$ and $\mathrm{F}$ are independent events.

(iii) In a standard 52-card deck, the queen, the king, and the jack are represented by four cards each.

Hence, $\mathrm{P}(\mathrm{E})=$ the card drawn is either king or queen $=8 / 52=2 / 13$

$\mathrm{P}(\mathrm{F})=$ the card drawn is either queen or jack $=8 / 52=2 / 13$

There are 4 cards which are either king or queen and either queen or jack.

$P(E \cap F)=$ the card draw $n$ is either king or queen and either queen or jack $=4 / 52=1 / 13$ $\ldots$ (1)

And $P(E) . P(F)$

$=2 / 13 \times 2 / 13=4 / 169 . \ldots .$

From (1) and (2)

$\Rightarrow P(E \cap F) \neq P(E) . P(F)$

Hence, $\mathrm{E}$ and $\mathrm{F}$ are not independent events.