Combinatorics

Mr 4meonly,
i don't know the formula to this problem, but I followed counting from the root level .

assume that,

n = -16, m = -15 ---- 1 possible
n = -16, m = -14------2 "
n = -16, m = -13------3 "
n = -16, m = -12------4 "

" " " " " " " " "
n = -16, m = 10------26 possible

sum all the values ;

n ( n+1 ) / 2 = 26* 27 /2 =13 * 27 = 351,

Hence the answer is B

correct me if I am wrong, thankyou

I did not follow through completely
What about for other values of N?
N=-15,-14........9

dendude wrote:I did not follow through completely
What about for other values of N?
N=-15,-14........9

Totally there are 27 numbers from -16 to 10

Now in n = -16, m could be any number from -15 to 10 i.e m will have 26 possible values

If n = -15, m could be any number from -14 to 10 i.e m will have 25 possible values

Similarly if n = -14, m can take 24 values

Thinking along the same lines if n = 9, m can take only 1 value.

Hence total number of possible ways = 1+2+.....+26 = 26X27/2 = 351

4meonly wrote:OA B

You need select m and N from 27 numbers.

Solution 1:
here order does matter:

No of ways selecting any two numbers = 27*26

In these combinations half of the time M >N and half of the time N>M

Ans = 27*26/2 = 351

Solution 2:

Select any two numbers from 27 list (order doesn't matter)
assume that greater number is m and other one is n
= 27C2
= 351

As noted above