The formula for percent error is : [tex]\frac { |Estimated\quad value\quad -\quad Exact\quad value| }{ |Exact\quad value| } \cdot 100[/tex].
So let's plug the given values in the formula.
[tex]\frac { |40-47| }{ |47| } \cdot 100=\quad \frac { |-7| }{ 47 } \cdot 100=\frac { 7 }{ 47 } \cdot 100=0.148\cdot 100=\frac { 148 }{ 1000 } \cdot 100=\frac { 148 }{ 10 } =14.8[/tex]
The percent error is 14.8%