Word Book

I bought an English word book for my son. My son is a middle school student and he isn't good at English. He is going to take a high school entrance exam next year. He doesn't have much time to prepare for the exam but he doesn't care much about that. 

I told him to memorize about 400 essential words. If he remembers these words, he would get 50 points in the English test. I really want him to be serious for the exam.