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When i add money am i supposed to make it like this 7+12 or 7.00+12.00 because i got 19 dollars for my answer

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

Kayaks rent for $35 per day. which expression can you use to find the cost in dollars of renting 3 kayaks for a day?