Here's how to use an Abacus [Japanese soroban]. My simple guide.
The basic skill is to be able of writing a number over an existing number. Which results in both getting added.
I won't cover the basics, as this is for those that already know the basics. Just the extra stuffs :
Here is the set of numbers you can write [1,2,3,4,5,6,7,8,9]
To add 5 :
Pull down the "5" bead.
If it's already down then pull that up and pull up a "1" on its left.
With case for 5 solved, we now have two set of remaining numbers [1,2,3,4] the low-number set, and [6,7,8,9] the high-number set.
Convert the high into one of low number reducing it by 5.
We now are down to [1,2,3,4].
Pull up that many bids of "1"s from bottom. And if the number was from high set, then also pull down the "5" form top following the rule describe first.
Can't pull up "1"s? Some of those might already be up. Then don't pull anything up. Rather pull down required "1"s as to complement the given number to 5. For example pull down 2 beads, if you can't pull up 3 beads. After that pull down the "5" as described above. Or pull up a "1" on the left column if the number was from the high number set without touching any "5".
Done. #Math #Abacus