JEE Advanced 2025 Chemistry question

Consider a reaction A + R ⟶ Product. The rate of this reaction is measured to be k[A][R]. At the start of the reaction, the concentration of R, , is 10-times the concentration of A, . 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]