(This post has been edited, based on feedback in comments that followed my initial posting)
According to KT Dict, when pronounced with the third tone, this shu3 is the verb, and means to count or enumerate, and to criticize (as in to enumerate one's shortcomings). So in keeping with the initial meaning of "Maths" given here in Memrise, I'm remembering it as "the Math of everything wrong about you!" as in the phrase, 数落 shu3 luo4, which also means to enumerate one's shortcomings, to criticize, to scold, and to talk on and on.
shu3 shu4 meaning to reckon
When pronounced with the 4th tone, this shu4 is a noun, and means number, figure, or several, and the example phrases are more literally mathematical:
shu4 wan4 being several tens of thousands,
shu4 zhu1 = rosary, prayer beads (beads to count the number of prayers)
shu4 ju4 = data/numbers/digital
shu4 nian2= many years
KTdict also indicates that this character may also be pronounced shuo4, in which case it means frequently or repeatedly.