题目

Fireflies flash not just for mating (交配), but survival, a new study suggests. Scientists wanted to find out if there’s more to the lightning bug’s signature blinking glow (一闪一闪的亮光) than finding a mate. Some experts had assumed it was a glaring signal to predators (捕食者), like bats, that fireflies taste bad.To test out whether the glow acted like that, researchers at Boise State University in Idaho put bats and fireflies in front of high-speed cameras. They published their results in Wednesday’s journal Science Advances.The painstaking experiment required researcher七年级（1）班数学兴趣小组的同学一起去租车秋游，预计租车费人均分摊1 8元，后来又有4名非兴趣小组同学要求加入，但租车费不变，结果每人可少摊3元，求七（1）班有多少名数学兴趣小组成员？