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Short Summary
Main recommendation: Learn the mental abacus, a technique where you visualize an abacus in your mind and move the virtual beads to add and subtract numbers at high speed, beginning with the finger abacus as a stepping stone. The speaker reports that after one week of practice they could handle addition and subtraction problems quickly, including a challenge with 200 numbers at 0.4 seconds each where he says he started calculating mentally about halfway through. The video also shares shortcut tricks for specific multiplication and addition problems.
Key Points
- The finger abacus uses both hands as an abacus: each finger on the right hand is worth 1 and each thumb is worth 5, while the left hand works the same way for tens, so a number can be held on the hands and counted without strain.
- Specific shortcuts exist: multiplying any two-digit number by 11 means splitting its digits, adding them, and placing the sum in the middle (53 × 11 = 583; carry the 1 if the sum exceeds 10, so 56 × 11 = 616).
- For two two-digit numbers with the same first digit whose second digits add up to 10, take the first digit times itself plus 1 as the front part and multiply the last digits for the end (27 × 23 = 621).
- Adding larger numbers can be simplified by splitting them into easier chunks (156 + 123: 156 + 100 = 256, then + 23 = 279), though the speaker notes this is still much slower than a calculator.
- Mental abacus is described in the video as notoriously difficult for adults and teenagers to learn, which is presented as why the experts in such videos started as children.
Details Worth Noting
- Concrete instructions:
- Finger abacus: start with fists closed; right hand = ones, left hand = tens. Each non-thumb finger adds 1 (10 on the left hand); each thumb adds 5 (50 on the left hand). Count up by extending fingers, then add the thumb for 5 through 9. Example: 36 + 23 = show 3 on the left and 6 on the right, add 20 and 3, get 59.
- Multiply by 11: split the two digits, add them, put the sum in the middle, carry 1 to the first digit if the sum is 10 or more.
- Same first digit, second digits summing to 10: multiply the first digit by (itself + 1) for the front, multiply the last digits for the end.
- Mental abacus: visualize the abacus, move beads mentally (earth bead up = +1, heaven bead down = +5 in each column), and keep the image stable while updating it. Practicing with physical hand motions can make the mental picture easier to control.
- The finger method caps out at 99 since it uses two hands.
- The speaker reports that after one week of practice they could handle addition and subtraction at speed, and that at the fastest speed (200 numbers at 0.4 seconds each) he says he started calculating mentally about halfway through.
Bottom Line
Mental abacus is a difficult but learnable skill, and the video's practical path starts with the finger abacus before moving to purely mental visualization.
