Mymensingh higher secondary 2015 #4

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samiul_samin
Posts:1007
Joined:Sat Dec 09, 2017 1:32 pm
Mymensingh higher secondary 2015 #4

Unread post by samiul_samin » Sun Feb 17, 2019 10:40 pm

In a bank there are $1000$ vaults. Of them first one is open, next two are closed, next three are open, and next four are closed, and so on… Total how many vaults are open then?

samiul_samin
Posts:1007
Joined:Sat Dec 09, 2017 1:32 pm

Re: Mymensingh higher secondary 2015 #4

Unread post by samiul_samin » Sun Feb 17, 2019 10:59 pm

Hint
$1+3+5+7=16$
Answer
$500^2=250000$

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