Question

用1+3+5+7+9+11+13+15+17+19分+别写出得数相等的加法和减法算式+每个数只能用？

Answer 1

1 + 3 = 4
1 + 5 = 6
1 + 7 = 8
1 + 9 = 10
1 + 11 = 12
1 + 13 = 14
1 + 15 = 16
1 + 17 = 18
1 + 19 = 20

3 + 5 = 8
3 + 7 = 10
3 + 9 = 12
3 + 11 = 14
3 + 13 = 16
3 + 15 = 18
3 + 17 = 20

5 + 7 = 12
5 + 9 = 14
5 + 11 = 16
5 + 13 = 18
5 + 15 = 20

7 + 9 = 16
7 + 11 = 18
7 + 13 = 20

9 + 11 = 20

15 - 1 = 14
17 - 1 = 16
19 - 1 = 18

15 - 3 = 12
17 - 3 = 14
19 - 3 = 16

15 - 5 = 10
17 - 5 = 12
19 - 5 = 14

15 - 7 = 8
17 - 7 = 10
19 - 7 = 12

15 - 9 = 6
17 - 9 = 8
19 - 9 = 10

15 - 11 = 4
17 - 11 = 6
19 - 11 = 8

15 - 13 = 2
17 - 13 = 4
19 - 13 = 6

15 - 17 = -2
19 - 17 = 2

15 - 19 = -4

Answer 2

1+3+5+7+9+11+13+15+17+19
=[（1+19）÷2]²
=[20÷2]²
=10²
=100