A worker is hired for $80 a day on the condition that if business is slow, the worker will only receive half pay.  At the end of 20 days, the worker receives $1,320.  On how many days was business slow?

7 slow daysYou know the worker worked a total of 20 days, some at $80 per day, and some at $40 per day.  After the 20 days, the worker was paid $1320.x = days paid full time ($80)y = days paid half time ($40)you have two unknowns, so you'll need two equations to solve, from the problem statement, we can derive the following relationships:($80)x + ($40)y = $1320x + y = 20 daysx = 20 - y80(20 - y) + 40y = 13201600 - 80y + 40y = 13201600 - 40y = 13201600 - 1320 = 40y280 = 40yy = 280/40 = 7thus 7 days paid half time (i.e. slow days)verify your solution is correcty = 7x = 20 - 7 = 1380(13) + 40(7) = 1320 [OK]