A scientist investigated the effect of a drug on the reaction times of three volunteers - Edexcel - GCSE Biology - Question 4 - 2014 - Paper 1

To find the missing reaction time for volunteer B, we first need to calculate the mean reaction time using the provided data.

The mean reaction time is calculated as follows:

$ext{Mean} = \frac{\text{Sum of reaction times}}{\text{Number of reactions}}$

Let the missing reaction time for B be represented as $x$.

We know that the mean reaction time for volunteer B is 40 ms. Therefore:

$40 = \frac{38 + 40 + x}{3}$

By multiplying through by 3:

$120 = 38 + 40 + x$

This simplifies to:

$120 = 78 + x$

Thus:

$x = 120 - 78 = 42$

Therefore, the missing reaction time for volunteer B is 42 ms.