Mom goes to the supermarket to buy drinks and finds that supermarket a is 10 yuan per bottle, buy four and get one free; supermarket b is 10 yuan per bottle, and sells it at a discounted price of 15%. How about buying 5 bottles?
妈妈到超市买饮料发现a超市每瓶10元，买四送一；b超市每瓶10元，按八五折优惠价销售，妈妈买2瓶饮料去哪个超市划算？买5瓶呢？
<result>5</result>