How do you write 4000 in scientific notation

Nnnnneeedd 1.find the residual if you know the actual number is 5.2 and the predicted value is 4.8

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?

Use the given information to determine the exact trigonometric value.