求告人指点!这道GMAT数学题的题目看不懂 :(

题目

求告人指点!这道GMAT数学题的题目看不懂 :(
原题：on a purchase of $120, a store offered a payment plan consisting of a $20 down payments of $10 each. What percent of the purchase price, to the nearest tenth of a percent, did the customer pay in interest by using this plan?
答案是16.7%
看不懂what percent 后面什么意思?什么nearest tenth of a percent?
如果是保留小数位的话是否需要四舍五入呢?

答案

to the nearest tenth of a percent是指精确到小数点后一位 如：16.7%,17.8% etc.题目意思是买了个120块钱的东西 你首付20 每个月付10块 问最后这个顾客选择这种（按揭）方法购买商品付出的利息/商品原价,即→利息=2...