15/22:21/44-1

Interpret the expression as (15/22) ÷ (21/44) − 1.

• (15/22) ÷ (21/44) = (15/22) × (44/21) = 660/462 = 10/7
• 10/7 − 1 = 10/7 − 7/7 = 3/7

Answer: 3/7

Note: If the colon was meant as something else, please specify.