Multiply. (2.5×10−10)(7×10−6) express your answer in scientific notation. 1.75×1016 1.75×10−15 1.75×10−16 1.75×10−17

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?