One drops five to four (4+ 1), two drops five to three (3+2, 4+2), three drops five to two (2+3, 3+3, 4+3) and four drops five to one (1+4, 2+4, 3+4).
One goes nine into one (9+ 1), two goes eight into one (8,9+2), three goes seven into one (7,8,9, +3), four goes six into one (6,7,8,9+4), five goes five into one (5,6,7,
Six go four into one (4+6, 9+6), seven go three into one (3+7, 4+7, 8+7, 9+7), eight go two into one (2+8, 3=8, 4+8), nine go one into one (1+9,
Six on one to five into one (5, 6, 7, 8+6), seven on two to five into one (5, 6, 7+7), eight on three to five into one (5, 6+8) and nine on four to five into one (5+9).
abacus
Abacus is an auxiliary tool for manual operation and calculation. It originated in China and has a history of more than 2,600 years. This is an important invention in ancient China. Before Arabic numerals appeared, abacus was a widely used computing tool in the world.
Now, abacus continues to be used in parts of Asia and the Middle East, especially in shops, which can be bought from shops that supply goods from China and Japan.
In the west, it is sometimes used to help children understand numbers. Some mathematicians like to experience the feeling of calculating simple arithmetic problems with an abacus.