A typist types (15) pages in the first hour and (5) more pages each next hour. How many pages are typed in (9) hours?

Correct answer: (315)

The correct answer is C, 315 pages. The hourly numbers form an arithmetic progression because the first term is 15 and each next term increases by 5. Thus the terms are 15, 20, 25, 30, 35, 40, 45, 50, and 55. For nine hours, use the sum formula \\(S_n=\\frac{n}{2}[2a+(n-1)d]\\). Here, \\(n=9\\), \\(a=15\\), and \\(d=5\\). Therefore, \\(S_9=\\frac{9}{2}[2(15)+8(5)]=\\frac{9}{2}(30+40)=\\frac{9}{2}\\times70=315\\). Option A, 285, is too small and results from an incorrect total. Option B, 300, does not equal the AP sum. Option C is correct because it includes all nine hourly outputs. Option D, 330, is too large and usually comes from adding an extra increase or using the wrong last term. Check also by pairing first and last terms: 15+55=70, and there are 4.5 pairs, giving 315. Memory cue: identify first term, common difference, and number of terms before using the sum formula.