三下五除二

ChineseEdit

three; 3

under; second; next; lower; below; underneath; down(wards); to decline; to go down; latter
five; 5

remove; do away with; wipe out; divide; except
two; 2
(三下五除二)
Literally: “three, down five, take away two”.

EtymologyEdit

A mnemonic device to aid with adding 3 to 2, 3 and 4 in base 10 (also 7, 8 and 9 in base 16).

• Ex. ${\displaystyle 3+3=6}$
2. Move one of the top beads down (each top bead is equal to 5).
3. Take away two of the beads from the bottom.
4. This leaves you with one top bead (5) and one bottom bead (1), for a total of 6.
Step 1 Step 2 Step 3

IdiomEdit

1. in an instant; in the blink of an eye; quickly and easily