The memo is a checklist, not a single answer
Every maths memo breaks a question into individual marking points — usually 'M' for method and 'A' for accuracy/answer. Markers work through your solution ticking off each point they can find, even if your final answer is wrong.
This means: always show your steps
Writing only the final answer, even if correct, forfeits every method mark attached to the working — often more marks than the answer itself is worth.
Conversely, if you make one small error partway through but keep working correctly from that point on, you can still pick up almost every remaining method mark — this is called 'error carried forward', and it's why giving up mid-question costs you marks you could have kept.
Practical takeaway
Never leave a question blank if you can write down even the first correct step — a formula, a substitution, a diagram. That first step alone is often worth a mark on its own.