<?xml version="1.0" encoding="utf-8"?><feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en_GB"><generator uri="https://jekyllrb.com/" version="3.10.0">Jekyll</generator><link href="https://mystemlab.co.uk/feed.xml" rel="self" type="application/atom+xml" /><link href="https://mystemlab.co.uk/" rel="alternate" type="text/html" hreflang="en_GB" /><updated>2026-08-18T09:07:35+00:00</updated><id>https://mystemlab.co.uk/feed.xml</id><title type="html">My STEM Lab</title><subtitle>Online 1-to-1 tuition in Maths, Further Maths, Physics and Computing, plus STEP, ESAT and TMUA preparation. Taught by Aarit Maheshwari — A* in Maths, Further Maths, Physics and Chemistry, grade 9 in every GCSE.</subtitle><entry><title type="html">TMUA Paper 2: necessary, sufficient, and why students lose marks here</title><link href="https://mystemlab.co.uk/blog/tmua-paper-2-necessary-and-sufficient/" rel="alternate" type="text/html" title="TMUA Paper 2: necessary, sufficient, and why students lose marks here" /><published>2026-08-16T00:00:00+00:00</published><updated>2026-08-16T00:00:00+00:00</updated><id>https://mystemlab.co.uk/blog/tmua-paper-2-necessary-and-sufficient</id><content type="html" xml:base="https://mystemlab.co.uk/blog/tmua-paper-2-necessary-and-sufficient/"><![CDATA[<p>Almost everyone preparing for the TMUA does the same thing: more A-Level questions. It’s the obvious
move and it barely helps, because the content on the TMUA is content you already know. The difficulty
is elsewhere — in the pace on Paper 1, and in the <strong>reasoning</strong> on Paper 2.</p>

<p>Paper 2 tests things A-Level never explicitly teaches. Here’s the one that costs the most marks.</p>

<h2 id="necessary-versus-sufficient">Necessary versus sufficient</h2>

<p>Take the statement:</p>

\[x &gt; 3 \implies x^2 &gt; 9\]

<p>This is true. Being greater than $3$ is <strong>sufficient</strong> for $x^2 &gt; 9$ — knowing it is enough to
conclude it.</p>

<p>But it is not <strong>necessary</strong>. $x = -5$ has $x^2 = 25 &gt; 9$ without $x &gt; 3$. So the converse fails:</p>

\[x^2 &gt; 9 \not\Rightarrow x &gt; 3\]

<p>The words are worth getting exactly right, because the exam uses them precisely:</p>

<ul>
  <li><strong>$P$ is sufficient for $Q$</strong> means $P \implies Q$. <em>If you have $P$, you’re done.</em></li>
  <li><strong>$P$ is necessary for $Q$</strong> means $Q \implies P$. <em>Without $P$, you can’t have $Q$.</em></li>
  <li><strong>$P$ is necessary and sufficient for $Q$</strong> means $P \iff Q$.</li>
</ul>

<p>A quick sanity check I find useful: <strong>sufficient conditions are small, necessary conditions are big.</strong>
A sufficient condition is a subset of the thing it implies — enough, but possibly more than enough.
A necessary condition is a superset — required, but possibly not enough on its own.</p>

<h2 id="where-the-marks-actually-go">Where the marks actually go</h2>

<p>The classic TMUA question gives you a statement and four candidate conditions, and asks which is
necessary but not sufficient. Students who know the definitions still get these wrong, for a
predictable reason: <strong>they check one direction and stop.</strong></p>

<p>So build the habit of always checking both, explicitly:</p>

<ol>
  <li>Does $P \implies Q$? If yes, $P$ is sufficient.</li>
  <li>Does $Q \implies P$? If yes, $P$ is necessary.</li>
  <li>Both? Necessary and sufficient. Neither? Neither.</li>
</ol>

<p>Two questions, every time. It takes ten seconds and it removes an entire category of error.</p>

<h2 id="negation-and-the-quantifier-trap">Negation, and the quantifier trap</h2>

<p>The other reliable mark-loser. What is the negation of:</p>

<blockquote>
  <p>For all real $x$, $f(x) &gt; 0$.</p>
</blockquote>

<p>It is <strong>not</strong> “for all real $x$, $f(x) \leq 0$.” That’s a much stronger claim.</p>

<p>The negation is:</p>

<blockquote>
  <p>There exists a real $x$ such that $f(x) \leq 0$.</p>
</blockquote>

<p>The rule: negating flips the quantifier as well as the statement. $\forall$ becomes $\exists$, and
$\exists$ becomes $\forall$. To disprove “all swans are white” you need one black swan, not a proof
that every swan is black.</p>

<p>This shows up constantly on Paper 2, and it’s the single highest-value thing to drill because the fix
is mechanical once you’ve seen it.</p>

<h2 id="finding-the-flaw-in-a-proof">Finding the flaw in a “proof”</h2>

<p>Paper 2 also gives you an argument that reaches a false conclusion and asks which line is wrong.
Three culprits cover most cases:</p>

<p><strong>Dividing by something that might be zero.</strong> The classic fake proof that $1 = 2$ divides by $a - b$
after assuming $a = b$.</p>

<p><strong>Squaring both sides.</strong> $x = -2$ becomes $x^2 = 4$, which now also permits $x = 2$. Squaring
introduces solutions; it doesn’t preserve equivalence.</p>

<p><strong>Assuming the converse.</strong> The argument proves $P \implies Q$ and then uses $Q \implies P$. This one
is deliberately hard to spot because the line reads perfectly naturally.</p>

<p>When you’re hunting, check every step that isn’t reversible. That’s where the flaw lives — almost
without exception.</p>

<h2 id="how-much-practice-is-enough">How much practice is enough</h2>

<p>Less than you’d think. This is a small, closed set of ideas, and a few hours of deliberate work on
them moves your Paper 2 score more than another twenty A-Level questions ever will.</p>

<p>Do real past papers, and after each one write down not just what you got wrong but <em>which</em> of these
patterns it was. The list is short enough that you’ll start recognising them cold within a fortnight.</p>

<div class="callout">
  <p>Free official TMUA past papers and worked solutions are linked on the
<a href="/subjects/tmua/">TMUA subject page</a>. Start with a full paper cold to get a
baseline — it’s uncomfortable, and it’s the most useful hour of preparation you’ll spend.</p>
</div>]]></content><author><name></name></author><category term="TMUA" /><category term="admissions tests" /><summary type="html"><![CDATA[Almost everyone preparing for the TMUA does the same thing: more A-Level questions. It’s the obvious move and it barely helps, because the content on the TMUA is content you already know. The difficulty is elsewhere — in the pace on Paper 1, and in the reasoning on Paper 2.]]></summary></entry><entry><title type="html">Five things to try when you’re completely stuck</title><link href="https://mystemlab.co.uk/blog/what-to-do-when-you-are-stuck/" rel="alternate" type="text/html" title="Five things to try when you’re completely stuck" /><published>2026-08-10T00:00:00+00:00</published><updated>2026-08-10T00:00:00+00:00</updated><id>https://mystemlab.co.uk/blog/what-to-do-when-you-are-stuck</id><content type="html" xml:base="https://mystemlab.co.uk/blog/what-to-do-when-you-are-stuck/"><![CDATA[<p>Most students treat being stuck as information about themselves. <em>I don’t get this. I’m not
a maths person.</em> It isn’t. Being stuck is information about the <strong>problem</strong> — specifically,
that you haven’t yet found the right way in.</p>

<p>Strong problem-solvers aren’t stuck less often. They’re just quicker to move through it, because
they have a list of things to try. Here’s mine.</p>

<h2 id="1-try-a-small-case">1. Try a small case</h2>

<p>If the question is about $n$, try $n = 1$. Then $n = 2$. Then $n = 3$.</p>

<p>This feels like cheating. It isn’t — it’s the single most productive move in mathematics.
Small cases show you the pattern, tell you what the answer should look like, and very often
reveal <em>why</em> the general statement is true.</p>

<p>Suppose you’re asked to show that</p>

\[1 + 2 + 3 + \cdots + n = \frac{n(n+1)}{2}\]

<p>and you can’t see where to begin. Write out $n=4$: $1+2+3+4 = 10$, and $\frac{4 \times 5}{2} = 10$.
Now pair the terms from the outside in: $1+4 = 5$ and $2+3 = 5$. Two pairs of $5$. There’s your proof,
and you found it by playing with a specific case rather than staring at the general one.</p>

<h2 id="2-draw-it">2. Draw it</h2>

<p>Even when it isn’t obviously a geometry question. Sketch the function. Draw the situation. Put the
vectors on a diagram with the angle marked.</p>

<p>A surprising proportion of “I don’t know how to start” is really “I haven’t formed a picture of what’s
going on”, and the picture usually suggests the method. In mechanics this is close to universal:
almost every mechanics question that goes wrong went wrong because there was no force diagram.</p>

<h2 id="3-name-what-you-want">3. Name what you want</h2>

<p>Write down, in words, the thing you’re trying to find. Then write it as a symbol.</p>

<p>It sounds trivial. It is astonishingly effective, because a lot of stuckness comes from holding too
much in your head at once. “I want the value of $k$ that makes the discriminant zero” is a sentence
you can act on. “I want to do question 7” isn’t.</p>

<h2 id="4-work-backwards-from-the-answer">4. Work backwards from the answer</h2>

<p>If the question tells you what to show — and in STEP, in proofs, and in “hence show that” questions,
it usually does — start from the target and ask what would be enough to get there.</p>

<p>To show $x = 3$, it would be enough to show $x - 3 = 0$. It would be enough to show that $x$ is a root
of some polynomial you can factorise. Now you have a smaller, more concrete goal than you started with.</p>

<h2 id="5-ask-what-youve-been-given-that-you-havent-used">5. Ask what you’ve been given that you haven’t used</h2>

<p>This is the one I use most in exams, and it’s nearly always the answer to a “hence” question.</p>

<p>Exam questions are constructed. Every condition in the stem is there for a reason. If you’ve reached
part (iii) and haven’t used the fact that the sequence is increasing, or that $n$ is even, or the result
you proved in part (i) — that unused fact is your next step. Part (i) of a STEP question is almost never
a warm-up. It’s the hint.</p>

<h2 id="the-habit-underneath-all-five">The habit underneath all five</h2>

<p>Notice that none of these require you to know more content. They’re all ways of changing your
<em>relationship</em> to the question — from “I must recall the method for this” to “let me find out what’s
going on here”.</p>

<p>That shift is most of what separates students who find maths frustrating from students who find it
interesting. It’s also entirely learnable, which is the good news.</p>

<div class="callout">
  <p><strong>Try this:</strong> next time you’re stuck for more than two minutes, work down the list rather than
re-reading the question a fourth time. Write down which one broke it open. After a few weeks you’ll
have a personal ranking — and reaching for it will have become automatic.</p>
</div>]]></content><author><name></name></author><category term="problem solving" /><category term="exam technique" /><summary type="html"><![CDATA[Most students treat being stuck as information about themselves. I don’t get this. I’m not a maths person. It isn’t. Being stuck is information about the problem — specifically, that you haven’t yet found the right way in.]]></summary></entry></feed>