largest middle digit

juantheron · 2011-12-17 05:37:27

Three digit no. are formed then what is the probability that middle digit is largest

bobbym · 2011-12-17 05:45:52

Hi;

juantheron · 2011-12-17 06:55:26

thanks bobbym

but how can you get the answer

would you like to explain here

bobbym · 2011-12-17 07:04:23

Hi;

Look at it like this:

0 or 1 in the middle is impossible for 2 then

{1} 2 {0,1} when 2 is in the middle there can be a 1 on the left and a 0 and 1 on the right 1*2 = 2.

{1,2} 3 {0,1,2} when 3 is in the middle there can be a 1,2 on the left and a 0
,1 and 2 on the right 2*6 = 6.

{1,2,3} 4 {0,1,2,3} when 4 is in the middle there can be a 1,2,3 on the left and a 0
,1,2 and 3 on the right 3*4 = 12.

The series is just a shorthand notation for this process continued till 9 is in the middle.

juantheron · 2011-12-17 07:17:06

Thanks bobbym got it (above give process)

but how can you write it in your answer

bobbym · 2011-12-17 07:22:57

Hi;

n = 8. Each term looks this (1*2)+(2*3)+(3*4)+(4*5)+(5*6)+(6*7)+(7*8)+(8*9)= 240

Each term is k(k+1) and there are 8 to be summed.

juantheron · 2011-12-17 07:25:47

thanks got it

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