<p cid="n0" mdtype="paragraph"><span style="font-size:18px;">These problems are mainly designed to be done once you've covered the entire foundation, as they can draw from other concepts too, which are not yet covered. For this reason, we've made them optional. Some of the questions can be done using only the foundation from the category the question belongs to, so you can give them a go if you like.</span></p>
<p cid="n16" mdtype="paragraph"><span style="font-size:18px;">If you find yourself struggling with these, that's perfectly normal, and you should skip them for now and retry them once your entire foundation is complete.</span></p>
