"Sagarika is never seen reading any Mathematics book during the daytime, yet she scored 98% marks in Mathematics. Therefore she must be studying during the night." Which means of knowledge is used in this argument?

Two facts that clash are reconciled by postulating a third, which is arthapatti.

Sagarika is never seen studying in the daytime, yet she scores very high marks.

These two observed facts cannot stand together without some explanation.

The only assumption that makes them consistent is that she studies at night.

This necessary supposition is arrived at, not by perception or inference, but by postulation.

Presuming an unseen fact to explain an otherwise inexplicable one is arthapatti (implication).