no. of ways in which we can choose 2 numbers such that there difference should be at most 10.The numbers must be between 1 and 100

hi ashish

there would 10 cases

when the difference b/w them is 1 then the set is {(1,2) , (2,3) .....(99,100)

there would be 99 cases

when the difference b/w them is 2 then the set is {(1,3),(2,4)....(98,100)

there would be 98 cases

similarly you can find it for the difference 3,4,5,6,7,8,9,10

they would be 97,96,......90

add all of them you will get the answer

90 + 91 +........99 = apply the A.P sum formula

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