Consider a reaction \( A + R \rightarrow \text{Product} \). The rate of this reaction is measured to be \( k[A][R] \). At the start of the reaction, the concentration of \( R \), \( [R]_0 \), is \( 10 \)-times the concentration of \( A \), \( [A]_0 \). The reaction can be considered to be a pseudo first order reaction with assumption that \( k[R] = k' \) is constant. Due to this assumption, the relative error (in \( \% \)) in the rate when this reaction is \( 40\% \) complete, is ________.
[\( k \) and \( k' \) represent corresponding rate constants]
