How many times is three times five divided by two? I know it's abacus. Please explain how it came about. Don't copy, but the language is easy to understand.

The abacus is divided into upper and lower gears, with the lower gear 1 beads representing 1 and the upper gear 1 beads representing 5.

When the abacus is empty, the number of beads in the lower gear is on the lower side of the lower gear and the number of beads in the upper gear is on the upper side of the upper gear.

Therefore, when adding 3, this formula is used when the number of beads above the lower gear is greater than or equal to 2. The next 5 is to dial 1 bead from the upper side to the lower side of the upper gear. Divide by 2, that is, dial 2 beads from the upper side of the lower gear to the lower side of the lower gear. This is three times five divided by two.

Because the formula is faster, it expands cleaner.