Infosys Company Logical Reasoning General Mental Ability

Sunny to pick as number of cards from a deck of cards. Sunny picks 1st card, another card by skipping 1 card, Picks another card by skipping two, so on skipping 1 card more each time. Ultimately he finds that he has picked up 5% of the cards. can you find out the no of cards?

Read Solution (Total 1)

(1),2 ,(3), 4, 5 ,(6),7 ,8, 9,(10), 11 ,12,13,14,(15).......so on
card no. inside the bracket will be selected
now n*(n+1)/2
if n=1 then n*(n+1)/2 = 1st card selected ,total card =1
if n=2 then n*(n+1)/2 = 3rd card is selected , total cards are 2
if n=3 then n*(n+1)/2 = 6th card is selected , total cards are 3
......................................../
.....................................so on
if n=n then n cards will be selected from n*(n+1)/2 cards

n
----------- *100= 5
n*(n+1)/2

n=39

hence total cards are 39(39+1)/2= 39*20= 780

thank you..
12 years agoHelpfull: Yes(1) No(1)

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