Climbing the first flight of stairs takes Jimmy 20 seconds, and each following flight takes 5 seconds more than the preceding one. How many total seconds does it take to climb the first five flights of stairs?
I need to find the sum of the times for the first five flights of stairs. I notice that the times form an arithmetic sequence, where each term is 5 seconds more than the previous one. I recall that the sum of an arithmetic series is given by the formula S_n = n/2 (a_1 + a_n), where n is the number of terms, a_1 is the first term, and a_n is the last term. Plugging these values into the formula, I get S_5 = 5/2 (20 + 40) = 150. Therefore, it takes Jimmy 150 seconds to climb the first five flights of stairs. 