The sixth grade students of an experimental primary school are divided into three groups to participate in tree planting activities. The number ratio of the first group and the second group is 5:4, and the number ratio of the second group and the third group is 3:2 It is known that the number of people in the first group is 15 less than that in the second and third groups. How many people participated in tree planting?

The sixth grade students of an experimental primary school are divided into three groups to participate in tree planting activities. The number ratio of the first group and the second group is 5:4, and the number ratio of the second group and the third group is 3:2 It is known that the number of people in the first group is 15 less than that in the second and third groups. How many people participated in tree planting?

15:12:8
15÷(12+8-15)=3
3×(12+8+15)=145