Related Clues:

• 41, for 20 and 21
• 5 + 5 = 10, for instance
• Greek characters returned amount
• Habit to drop cold summer's activity
• Abacus calculation
• Zero-__ game
• 758, for 145 + 308 + 305
• Everything is left out of poor-quality housing
• Many a bottom line
• ___ total
• What a capital sigma symbolizes, in math
• Tot in poor area beginning to lose out
• Homophone of 'some'
• "Cogito ergo ___"
• Σ, in math