Danny,
you do not need to.
starting with "one", which obviously is not the answer, go through the numbers up to twelve. The teens cannot be the answer, nor can twenty, therefore any of the twenties, or thirty or the thirties, so we next reach forty - i.e. only the 16th number you need to consider. Easily deduced within 30 seconds.
nescio//easily deduced within 30 seconds.//
My maths is obviously not up to your standard as I would never have thought of that method of arriving at the answer.Maybe I should not have left school ar the age of fourteen.
everyone's mind works in a different way.
The question a couple of weeks ago about the next book title exasperated me. The first words of the four previous books was given as a possible answer, but otherwise, there was no logical progression from the titles to suggest that was the answer, without it being given as an option.
a lesser amount, yes, but you cannot say a fewer amount.
Like the checkout at some supermarkets - for 10 items or fewer (not less) is correct, because few relates to a number of discrete entities. Less is used for a continuously variable amount. You cannot have say, 4.72 items, but you could have 4.72kg of a product.