This is the 2860th most frequent Japanese word.
ごく
"ごく" means "extremely" or "very."
Here, ごく is used to intensify 普通 (average, ordinary), emphasizing the common or typical nature of the subject in the statement.
彼の実績はごく普通である。
His performance is quite average.
In this case, ごく modifies 一部 (a part), indicating a very small segment or fraction, emphasizing the limited scope.
ごく一部の人々しかその実験に参加していない。
Only a very small portion of people participated in the experiment.
For this sentence, ごく intensifies 簡単 (simple, easy), suggesting a high degree of simplicity or ease in solving the problem.