Question

what do you understand by combination of resistance

Answer 1

combination of resistance means combination of obstruction takes place during flow of current

Answer 2

As resistance means that oppose flow of current.
And combination of resistance means when two or more than two resistance are join in parallel or series forms the combination of resostance. Which all oppose the flow of current on different ways. As when combine in series overall resistance increases while in parallel it decreases.
Hope it will help you. And no need to learn it just read and think for once or twice.