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The sequence 12, 15, 18, 21, 51, 81, ... contains all positive multiples of 3 that contain at least one digit that is a 1.  What is the 50th term of the sequence?

 Nov 14, 2019
 #1
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There may be an easier way to do this, but I would just go through the multiples and find them.

 

12, 15, 18, 21, 51, 81, 102, 105, 108, 111

114, 117, 120, 123, 126, 129, 132, 135, 138, 141

144, 147, 150, 153, 156, 159, 162, 165, 168, 171

174, 177, 180, 183, 186, 189, 192, 195, 198, 201

210, 213, 216, 219, 231, 261, 291, 312, 315, 318.

 Nov 14, 2019
 #2
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Nth Term =F + (D*(N-1)), where F=First term, D=Common difference, N=Nth term

                   =12 + (3*(50 -1))

                   =12 + (3 * 49)

                   =12 +   147

                   =159 - the 50th term.

 Nov 14, 2019

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