| Exam Board | OCR MEI |
|---|---|
| Module | AS Paper 2 (AS Paper 2) |
| Year | 2022 |
| Session | June |
| Marks | 1 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Discrete Probability Distributions |
| Type | One unknown from sum constraint only |
| Difficulty | Easy -1.8 This is a trivial application of the fundamental probability axiom that probabilities sum to 1. It requires only one step: subtract the given probabilities from 1. No problem-solving, conceptual understanding, or multi-step reasoning is needed—purely mechanical arithmetic. |
| Spec | 2.04a Discrete probability distributions |
| \(x\) | 1 | 2 | 3 | 4 | 5 |
| \(\mathrm { P } ( \mathrm { X } = \mathrm { x } )\) | 0.2 | 0.15 | \(a\) | 0.27 | 0.14 |
| Answer | Marks | Guidance |
|---|---|---|
| \(a = 0.24\) | B1 | CHECK additional pages; NB \(0.2 + 0.15 + a + 0.27 + 0.14 = 1\) |
## Question 1:
$a = 0.24$ | **B1** | CHECK additional pages; NB $0.2 + 0.15 + a + 0.27 + 0.14 = 1$
---1 The probability distribution for the discrete random variable $X$ is shown below.
\begin{center}
\begin{tabular}{ | c | c | c | c | c | c | }
\hline
$x$ & 1 & 2 & 3 & 4 & 5 \\
\hline
$\mathrm { P } ( \mathrm { X } = \mathrm { x } )$ & 0.2 & 0.15 & $a$ & 0.27 & 0.14 \\
\hline
\end{tabular}
\end{center}
Find the value of $a$.
\hfill \mbox{\textit{OCR MEI AS Paper 2 2022 Q1 [1]}}