!!PROBABILTY

If a and b are +ve integers.......find the probabilty that \frac{1}{2}(a^{2}+b^{2}) is a +ve integer

17 Answers

62
Lokesh Verma ·

if that is the case then you have to look at the integers a, b

they are of the form 5n or 5n+1 or 5n+4 or 5n+4 or 5n+1 depending on a/b being of the form 5n or 5n+1 or 5n+2 or 5n+3 or 5n+4

Then, to get the sum as a multiple of 5, we have to add particular kind of numbers..

Can you think the rest?

3
Swami Dayal ·

oh yeah thanx all

62
Lokesh Verma ·

now it is correct [1]

1
akari ·

i am extremely sorry i found out the answer for expression \frac{a^5 +b^5}{5}

if we proceed by same way
the possible combinations are
(5k,5l),(5k+1,5k+2),(5l+1,5k+2),(5k+1,5l+3),(5l+1,5k+3),(5k+4,5l+3),(5l+1,5k+3),(5k+2,5l+4),(5l+2,5k+4).
so 9 favourable cases
total combination is 25
so answer is
9/25

62
Lokesh Verma ·

this much is corect.. but then are you adding the numbers or their squares?

the squares are never of the form 5k+2 and 5k+3

62
Lokesh Verma ·

the answer is indeed 9/25

you should check for some missed cases..

62
Lokesh Verma ·

the answer is indeed 9/25

you should check for some missed cases..

62
Lokesh Verma ·

akari.. your soln is incorrect...

11
Devil ·

The key is to check the last digit of squares in this regard.

11
virang1 Jhaveri ·

1/2

3
Swami Dayal ·

oh my bad....................SO soryy for that ya its 5 IN THE DENOMINATOR

62
Lokesh Verma ·

Is this the question?

\frac{a^2+b^2}{5}

3
Swami Dayal ·

no thats not the ans !!!!.........ans is 9/25

1
Nikhil Kaushik ·

what is the correct answer.........& how are you not sure that 1/2 is not the correct answer?

3
Swami Dayal ·

i dunno the ans.....can u all plz show ur working

1
Avinav Prakash ·

is the ans- 4/9??

3
Swami Dayal ·

nope thats not the ans.......

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