5. Garden workers need to dig holes at equal distances along the edge of a circular flower bed with a circumference of 300 meters. They started digging holes every 3 meters along the edge of the flower bed. When they had dug 30 holes, they received instructions from their superiors to change to planting trees every 5 meters. How many more holes do they need to dig to complete the task?
【Answer】 54
【Analysis】Exam point: Tree planting problem
$300 \div 5=60 ; 3 \times(30-1)=87 ; 0,15,30,45,60,75$ (repeated) a total of 6; still need to dig 60 $-6=54$ holes