in Quantitative Aptitude retagged by
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A book contains $100$ pages. A page is chosen at random. What is the chance that the sum of the digits on the page is equal to $8$?

  1. $0.08$
  2. $0.09$
  3. $0.90$
  4. $0.10$
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4 Comments

(1,7)(7,1)(2,6)(6,2)(3,5)(5,3)(4,4) and page number 8 itself are the total possible combinations.Shouldn't answer be 0.08
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Why not

80 and 08 ??
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Ohh....I forgot 80 :)
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2 Answers

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Best answer
Note:- single digit page 8 can be written in 2 digit as 08.

the sum of two digits should be 8.

$x+y = 8, x1,x2>=0$

$C(n+r-1,r) = C(2+8-1,8)=C(9,8) =9$

Required probability = $\frac{9}{100} = 0.09$

Hence, (B) is the correct option!
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3 Comments

Ans is 0.09 Right , But how you uses combination for this please explain?
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@bhanu kumar 1 number of non negative integral solutions.

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edited by
Yes.Combinations are useful for larger values too.
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chance that the sum of the digits on the page is equal to 8 are:-

8 ,17,26,35,44,53,62,71,80

so, ans= 9/100 = 0.09
Answer:

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