The property that justifies the sentence 2x^2+(5x*+1)=(2x^2+5>+1

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?

How is the interquartile range calculated?

You use technology ans find a sum of 6.712e-8. write this sum in standard form