Question

Jerry started doing sit-ups every day. The first day he did 16 sit-ups. Every day after that he did 2 more sit-ups than he had done the previous day. Today Jerry did 22 sit-ups. Enter an equation that could be solved to find the number of days Jerry has been doing sit-ups, not counting the first day. The equation d + = can help find the number of days Jerry has been doing sit-ups.

Answer 1

Let s and d represent the number of sit-ups Jerry does and the number of days Jerry has been doing them (not counting the first), respectively. The problem statement tells us
  s = 16 + 2d
This is the equation that can be solved to find d.

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Here is its solution.
Since we want to find d (the number of days), we can subtract 16 and divide by 2.
  s - 16 = 2d
  (s - 16)/2 = d
  d = (s/2) - 8
Example:
  Today Jerry did 22 sit-ups. He has been doing them for ...
  (22/2) - 8 = 11 - 8 = 3 . . . days