Question 1134943
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The other tutor mistakenly used the formulas for geometric series instead of arithmetic series....<br>
The last term is 9 times the first term, so we can call the first and last terms a and 9a.<br>
The average of the terms in an arithmetic sequence is the average of the first and last terms, so the average of the terms in the sequence is 5a.<br>
The sum of the terms of an arithmetic series is the average of the terms, multiplied by the number of terms.  Since the sum of the terms is 100 times the first term, the number of terms n can be found with<br>
{{{100a = 5a(n)}}}
{{{n = 20}}}<br>
There are 20 terms in the series.