Percentage decrease is 98.1%.
$\text{% decrease} = \dfrac{ \color{blue}{ \text{initial value} } - \color{red}{ \text{final value} }}{ \color{blue}{ \text{initial value} } } \times 100$ | $$ \begin{aligned} \color{blue}{ \text{initial value} } &= 100 \\[1.5em] \color{red}{ \text{final value} } &= 1.9 \end{aligned} $$ |
$\text{% decrease} = \dfrac{ \color{blue}{ 100 } - \color{red}{ 1.9 } }{ \color{blue}{ 100 } } \times 100 $ | |
$\text{% decrease} = 0.981 \times 100 $ | |
$\text{% decrease} = 98.1 \% $ |