Abacus Level 2: Big friends

What you’ll learn

• Big friends are pairs that make 10: 1 & 9, 2 & 8, 3 & 7, 4 & 6, 5 & 5
• Carry to the next rod while adding, borrow while subtracting
• 2-digit sums with 3–4 rows

Big friend formulas

• +1 = −9 +10
• +2 = −8 +10
• +3 = −7 +10
• +4 = −6 +10
• +5 = −5 +10
• +6 = −4 +10
• +7 = −3 +10
• +8 = −2 +10
• +9 = −1 +10
• −1 = +9 −10
• −2 = +8 −10
• −3 = +7 −10
• −4 = +6 −10
• −5 = +5 −10
• −6 = +4 −10
• −7 = +3 −10
• −8 = +2 −10
• −9 = +1 −10

▶ Watch it on the abacus

7 + 5 = 12: +5 = −5 +10 → take 5 away (2), then add 1 on the tens rod (12).

✏️ Practice

Work the sum on the abacus and press Check (or type the answer). Stuck? “Show me how”.

🏁 Level 2 test

20 sums. Work each sum on the abacus, press Check, then go to the next one. Get 16 or more right to pass the level.

🎓 Sign in with Google to get a certificate and the 🤝 Big Friends Pro badge when you pass. You can still take the test without signing in.

🖨️ Level 2 worksheets

• Worksheet set 1
• Worksheet set 2
• Worksheet set 3