Скачать или смотреть Lesson 4: Addition using 5's Complements

In Abacus we have only 5 beads on a column to count and operate numbers from 1 to 9. In that case, we are going to need the use of complements. We remember the complements in pairs. In this video, we are going to see the use of 5's Complement to do an addition. In case, we do not have enough beads and we have 5 available to add we can use its complement to do the addition. In fact, if the addend is 1, 2, 3, or 4 AND we see 5 is available to add, we can quickly decide to use the 5's Complement. Going by the formula We add 5 and subtract the 5 's complement of the addend. The process of understanding this to decide the applicable formula encourages the reasoning skills of the student.