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+16 votes
A deck of $5$ cards (each carrying a distinct number from $1$ to $5$) is shuffled thoroughly. Two cards are then removed one at a time from the deck. What is the probability that the two cards are selected with the number on the first card being one higher than the number on the second card?

  1. $\left(\dfrac{1}{5}\right)$

  2. $\left(\dfrac{4}{25}\right)$

  3. $\left(\dfrac{1}{4}\right)$

  4. $\left(\dfrac{2}{5}\right)$
asked in Probability by Veteran (106k points)
edited by | 2.2k views

4 Answers

+31 votes
Best answer

The number on the first card needs to be One higher than that on the second card, so possibilities are :

1^{\text{st}} \text{ card} & 2^{\text{nd}} \text{ card}\\
\color{red}1 & \color{red}-\\
2 & 1\\
3 & 2\\
4 & 3\\
5 & 4\\
\color{red}- & \color{red}5
\text{Total $:4$ possibilities}

Total possible ways of picking up the cards $= 5 \times 4 = 20$

Thus, the required Probability $= \dfrac{\text{favorable ways}}{\text{total possible ways}}=  \dfrac{4}{20} = \dfrac 15$

Option A is correct

answered by Boss (30.8k points)
selected by
How to solve the question if it would be only HIGHER and not ONE HIGHER?

How to solve the question if it would be only HIGHER and not ONE HIGHER?

 Possible combinations :-

First card second card
5 4,3,2,1
4 3,2,1
3 2,1
2 1
1 none

$P(First\ card\ is\ HIGHER\ than\ second\ one\ )=\left [ \left ( \frac{1}{5} \times \frac{4}{4}\right ) + \left ( \frac{1}{5} \times \frac{3}{4}\right ) + \left ( \frac{1}{5} \times \frac{2}{4}\right ) + \left ( \frac{1}{5} \times \frac{1}{4}\right ) \right]\\ =\frac{1}{2}$

Got it
+10 votes
Here we should consider without replacement, since "removed one at a time" means the card has been removed from the deck.

Prob of picking the first card  = 1/5

Now there are 4 cards in the deck. Prob of picking the second card = 1/4

Possible favourable combinations = 2-1, 3-2, 4-3, 5-4

Probability of each combination = (1/5)*(1/4) = 1/20

Hence answer = 4*1/20 = 1/5
answered by Active (1.2k points)
+5 votes
with 5 cards to choose we can only fulfil the condition if we pick 2,3,4,5 in our choice else theres no way to get the same

so 4/(5*4) is the answer
answered by Boss (14.4k points)
+2 votes
the probability of choosing first no's is =(2,3,4,5)/(1,2,3,4,5)=4/5

the second time, we have only one option to choose out of four option=1/4

so,the total probability=(4/5)*(1/4)=1/5
answered by (61 points)

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