4 min read
2026-01-28
10% of 50 = 50% of 10 = 5. Pick the order that is easier to compute.
Move the decimal one place left:
10% of 850 = 85
10% of 1230 = 123
Break tricky percents into easy ones:
15% = 10% + 5%
25% = divide by 4
75% = 50% + 25%
Estimate doubling time for an investment: **72 / annual rate ≈ years to double**.
Example: at 8% per year, money doubles in about 72/8 = 9 years.
Compare two “percent of” values on the same base:
30% of 200 vs 20% of 350
60 vs 70 → the second is larger
For exact finance (loans, taxes, investments), always use a calculator — a tenth of a percent can cost a lot.
See also: Scientific Calculator, Tip Calculator