edited by
908 views
2 votes
2 votes

 

How to do this question ..please help me guys

edited by

2 Answers

Best answer
2 votes
2 votes
Suppose you draw a single card, what number do you expect on it?? Let's calculate that first.

it would be, 1/80 * 1 +  1/80 * 2 + 1/80 *3 +.............................. 1/80 * 80

= 1/80 * (80 *81)/2

=40.5

So if you select one card out of 80 cards expected number on it is 40.5

For 30 cards, the Expected value will be, 40.5 *30 =1215
selected by
2 votes
2 votes
$\text{Total Numbered Cards} = 80$

$\text{Probability of a card being picked} = \Large \frac{3}{8}$

$E[x] = \sum_{i=1}^{k}x_i p_i$

$E[x] =\large  \frac{3}{8} \times 1 + \frac{3}{8} \times 2 + \frac{3}{8} \times 3 +...+\frac{3}{8} \times 80$

$E[x] = \frac{3}{8} \times \left ( 1 + 2 + 3 + 4 +...+80 \right )$

$E[x] = \large \frac{3}{8} \times \left ( \frac{80 \times 81}{2} \right )$

$E[x] = 1215$

Related questions

0 votes
0 votes
2 answers
1
radha gogia asked Feb 2, 2016
3,344 views
I did it from conditional probability , first case when we pick one spade first and then pick king nextso it is equal to ,probability of picking up a spade*probability o...
1 votes
1 votes
1 answer
3
Sahil Gupta asked Nov 24, 2014
4,407 views
The answer is 14.But there are four kind of cards.(spades,heart,diamond,chidi)So there must be 5 pick up to ensure the same kind condition.