Nikhilam Sutra
All from nine and the last from ten (nik · hi · lam)
What it means
Multiply two numbers that are both close to a round number like 100 or 1000 — without long multiplication. Measure how far each one falls short of the round number; use those two shortages to build the answer in one step.
Worked example
Multiply 97 × 98. Each number falls a little short of 100. 97 is short by 3; 98 is short by 2. Cross-subtract one shortage from the other: 97 − 2 = 95. Multiply the two shortages: 3 × 2 = 6. Put them side by side: 9506. Four seconds.