Optellen tot 1000 (HTE + T = HTE) - oefening 2

Optellen tot 1000... hoe doe je dat?
643 + 80 = ( 643 + ) + =
872 + 40 = ( 872 + ) + =
594 + 60 = ( 594 + ) + =
763 + 90 = ( 763 + ) + =
249 + 80 = ( 249 + ) + =