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a 4 digit number(numbered from 0000 to 9999) is said to be lucky if sum of its first two digits is same as the sum of its last 2 digits.If a four-digit number is picked up at random,the probability that it is a lucky number is????
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7 Answers
262i am getting 48910000
(tell me if i am very close to the ans.)
262yes, even i am getting 670 /10000
for sum of first 2 digits=k , (k≤9)
first digit can be chosen in (k+1) ways
and 2nd digit in 1 way.
third digit again in (k+1) ways,
and 4th digit in 1 way = (k+1)2 ways
for sum =k (18≥k>9)
first digit can be chosen in (19-k) ways
and 2nd digit in 1 way.
third digit again in (19-k) ways,
and 4th digit in 1 way = (19-k)2 ways
hence summing up , favourable cases = 12+22 + .....+82 +92 +82+....12 = 670
hence probability = 670 /10000