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Total number of ways of selecting two numbers from the set {1,2,3,4.....,90} so that their sum is divisible by3, is A. 885 1335 1770 3670

Total number of ways of selecting two numbers from the set {1,2,3,4.....,90} so that their sum is divisible by3, is
 
     A. 885
  1. 1335
  2. 1770
  3. 3670
 

Grade:11

1 Answers

haroon
10 Points
7 years ago
1335.   Select two numbers both div by 3  30c2 + one no from set 1,4,7... and one from 2,5,8... -- 30c1 *30c1  so total is 1335

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