③大拇指指中u2.算一算。$$ 58 \times 12=19 $$$ 3 4 \times 1 8 = 3 9 \times 2 0 = 6 7 \times 1 8 = 7 3 \times 1 9 = $$800$$ 49 \times 20=990 15 \times 28= $$$ 2 9 \times 1 4 = 2 8 \times 4 0 = $$120$$ 16 \times 50=800 $$ 190$$ 60 ...