Birdwatching Every Day!

Probability Level 1

Old Man Jon has retired rich, and has decided to spend his fortune to travel around the world birdwatching.

Every day, for the next one year, he will visit one location around the globe.

On the first day, he sees 1 bird. This number of birds he sees increases by one every day, so the number that he sees is the same as the day of the year. For example, on the 29th day, he saw 29 birds.

How many birds would he have seen by the end of the year?

66795 133225 83333 66612

Jay Steller by Jay Steller , 20, India

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5 solutions

Ravik Ganguly
Apr 17, 2014

Every day he sees 1 bird and the number of birds goes on increasing as the number of day. Therefore, Total birds = 1+2+3+4+5+.......+365 = .5*365(365+1) = 66795

3 Helpful 0 Interesting 0 Brilliant 0 Confused

YOU MUST MENTION THAT IT IS A LEAP YEAR

Kushagra Sahni - 7 years, 1 month ago

Hello,

as you know, a year = 365 days , and from the problem stated that it is increasing by 1(number of birds for each day) till the end of the year,

so, it is an arithmetic progression,

as a =1 , d =1 ,

S(365) = 365 /2 [ 2(1) + (364)(1)]

S(365) = 182.5(366) = 66795,

therefore, the number of birds = 66795...

2 Helpful 0 Interesting 0 Brilliant 0 Confused

[1+2+3+4+...+365]=66795

Is Xavier - 7 years, 1 month ago

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yes bro...

MOHD NAIM MOHD AMIN - 7 years ago

Sn=n/2[2a+n-1}d

S365 = 365/2{2x1 + (365-1)1 

        = 365/2{2 + 364}

        = 365x366/2

        = 365x183

        = 66795
0 Helpful 0 Interesting 0 Brilliant 0 Confused
Apurv Rajput
May 12, 2014

By the formula n(n+1)/2, where n=total no. of days=1 year =365 days, No.of birds watched = 365(365+1)/2 =133590/2 =66795

0 Helpful 0 Interesting 0 Brilliant 0 Confused
Aashish Patel
Apr 19, 2014

We can follow the series 1- - - - - - -- - - - - -- 365=1/2*365[365+1].=66795.total birds watched are 66795.

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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