Well geometry was more painful than math for the way they taught it in my school :-) Demonstrate that these two triangles are identical … cmon you could see that ;-) ;-)

For your last sum MY way of solving it (I think its 10.000 right ?) was noticing that I could add 1 to the second 99 and have 100, 2 to the subsequent 98 and so on and that these sums are 100, hence 100 times 100.

Not sure of what mental path I took.

What could be very useful, if at all possible, is to devise a sort of a standard test for your attitudes in math/logic and with that suggest what is the learning style for math that better suits your capabilities.