① 18/17÷19+1/19×16/17
=18/17×1/19+1/19×16/17
=1/19 ×(18/17+16/17)
=1/19 × 2
=2/19
② (2/3+4/15×5/2)÷20/21
=(2/3 + 2/3)× 21/20
= 4/3 × 21/20
= 7/5
③ 0.25×1.25×48
= 1/4 × 5/4 ×48
= 5/16 × 48
= 15
① 18/17÷19+1/19×16/17
=18/17×1/19+1/19×16/17
=1/19 ×(18/17+16/17)
=1/19 × 2
=2/19
② (2/3+4/15×5/2)÷20/21
=(2/3 + 2/3)× 21/20
= 4/3 × 21/20
= 7/5
③ 0.25×1.25×48
= 1/4 × 5/4 ×48
= 5/16 × 48
= 15