你查一下《韦氏高阶》,你会发现percent可以是可数名词,此时percent单复数同形。percent也可以是单数用词,与不定冠词连用。例如词典例句:
The value has increased half a percent. 可数名词单数
Water covers more than 70 percent of the Earth's surface. 可数名词复数
A large percent [=(more commonly) percentage] of their profits comes from online sales. 单数名词
所以,当表达一个百分数占比很大或很小时,常用单数名词percent,如 a small/large percent of something. 下面COCA语料库中percent前用不定冠词a时,通常都有表示多或者少意义的形容词,此时percent为单数名词用法,不是可数名词。
A whopping seventy-eight percent of water in the country
A full 20 percent of the 100 senators in January will be women
a reasonable 4.6 percent of the capital budget.
a mere 0.1 percent of the popular vote.
and a whopping 72 percent of those polled approved of the move.
unlike a full 40 percent of Les Miles victories
你的句子中,形容词merely意为仅仅,表示少的意思,所以percent在此为单数名词,与不定冠词连用。句子没有问题。