①: 10+20+....+80=360 ?
2 10*2-360=60
(It is enough to allocate 60, so the middle allocation is determined to be 20,40. )
②:2 10-60= 150
(The remaining numbers are: 10, 30, 50, 60, 70, 80; As long as the sum of three numbers on one side is equal to 150)