You probably multiplied the numbers and the powers of 10 correctly to get $\displaystyle{0.317}\times{{10}}^{{3}}\usepackage{cmbright}\Huge\$ . However, when you converted 0.317 to $\displaystyle{3.17}\times{{10}}^{{-{{1}}}}\usepackage{cmbright}\Huge\$ , you did not multiply the powers of 10 together to find $\displaystyle{3.17}\times{\left({{10}}^{{-{{1}}}}\times{{10}}^{{3}}\right)}\usepackage{cmbright}\Huge\$ .