Appendix C - Exercise Set - Page 746: 27

$0.0000000000000000028$

$(4\times10^{-10})(7\times10^{-9})$ $\longrightarrow$ associative property =$(4\times7)(10^{-10}\times10^{-9})$ $\longrightarrow$ multiply; add exponents if the base is the same =$28\times10^{-19}$ $\longrightarrow$ move the decimal 19 places to the left =$0.0000000000000000028$