It took me some while to get to the answer, so I was wondering if there was a shorter way to solve it. It’s from the BMAT 2020 (Q24)
Thanks in advance! 
Hi!
As all of the products have 1 saddle apart from the tandem, the fact that 10 saddles were used for 7 cycles shows that 3 tandems were built. If the saddles are removed , wheels and handlebars for 3 tandems from the totals shows that 4 saddles, 8 wheels and 3 handlebars were used to make the remaining 4 cycles. Since the unicycle does not have a handlebar, but the other two products have it, it must be the case that 1 unicycle was built. The remaining three cycles needed 7 wheels. If they had all been bicycles, then only 6 wheels would have been needed, so 1 tricycle must have been built, which option B is the answer.
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