Japanese Math 100

100 = 1+2+3+4+5+6+78+9
= 1+23-4+56+7+8+9
= 12+3-4+5+67+8+9
= 123+45-67+8-9
= 123-45-67+89
Or reverse
100 = 98+7+6-5-4-3+2-1
= 98-7+6+5+4-3-2-1
= 9+8+76+5-4+3+2+1
= 9-8+76-5+4+3+21
= 98-76+54+3+21