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Big Brother

📘What it is

The Big Brother method — adding through 5! Add 5, then subtract the extra. The secret of the 5-bead!

🛠️How it works

8+3 = 8+5-2 = 11. Add 5, then subtract 2!

🔢A worked example

In 4 + 3 there are not enough lower beads. The big brother — 5 — helps out: add 5 but remove the extra 2 (since 3 = 5 − 2) → 4 + 3 = 7.

🎓A closer look

Big Brother is the rule for the upper five-bead. When you need to add a number from 1 to 4 but the lower beads have run out, the formula is: add 5, then subtract the excess — that number's friend of five. For 4+2 there are no free lower beads, so 4+5−3=6 (the friend of 2 up to five is 3). In 13+4 three ones-beads are already in use: 13+5−1=17. Subtraction mirrors it: 7−3 = 7−5+2 = 4.

The rule works entirely inside one column — no carry into the tens is needed — which is why it is learned before Big Friends. Splitting numbers around 5 teaches a child to see the composition of a number and prepares them for the more advanced formulas built around 10 and 100.

Level: right after Small Friends (operations within 5).
Common mistake: subtracting the friend of ten instead of the friend of five.
Practice tip: drill each of the four cases separately: +1, +2, +3 and +4 through the five-bead.

💡Why it helps

This technique teaches working with the 5-bead on the soroban — just like the pros!

❓Frequently asked questions

Big Brother is a way of adding quickly using the upper five-bead on the soroban. Instead of four lower beads, the child moves a single five-bead to make up a number.

Because when adding a larger number such as 4 or 5, the child enters it in one move of the big brother rather than sliding four beads separately, which saves time.

This technique is learned once the child confidently sees numbers and works with the lower beads of the abacus, that is after grasping the basics.

Yes, on MentalMath you can learn the Big Brother technique and practise for free, with no registration needed.

Other methods

🧮 Abacus (Soroban) — the foundation of mental arithmetic 🔟 Friend of 10 🤝 Big Friends 🌉 Bridge to 10 ✨ ×11 Magic 9️⃣ ×9 Technique 🕛 ×12 Technique 🕉️ Vedic Math (100) 🔱 Vedic Math (1000) ✖️ Urdhva-Tiryagbhyam — vertical and crosswise multiplication 🔲 Squaring a number — the fast way ➗ Division

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