TWO MATHCOUNTS PROBLEMS I NEED HELP WITH: BEST THE ONE THAT HAS ALL THE ANSWERS!

Mathematics
Tutor: None Selected Time limit: 1 Day

221. If the counting numbers are written in order, what is the value of the 2015th digit written?

227. A sequence begins 1, 2, …, and each term after the second term is the sum of all preceding terms. What is the 15th term of this sequence?

Jun 7th, 2015

227. 1,2,3,6 --------

nth term = (n-1)(n)/2 

hence 15th term = 14*15/2 = 105

Jun 7th, 2015

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