Explore a fictional human-to-vampire age rule with an animated pair of timelines. Build the formula from its anchor and ten-to-one change, calculate 30 → 220, and reverse the result.
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The calculation
For the page's fictional scale, V = (H − 18) × 10 + 100; inverse H = (V − 100) ÷ 10 + 18. H and V are years on different invented scales, anchored at H = 18 ↔ V = 100.
Worked example
At H = 30, the span after the anchor is 30 − 18 = 12 human years. Multiply by 10 vampire years per human year: 12 × 10 = 120. Add the starting 100 vampire years to get V = 220. Reverse: (220 − 100) ÷ 10 + 18 = 30.
This conversion is a fictional convention defined by the linked page, not a biological or universal vampire-aging fact. The anchor is at human age 18; applying the line below that point is extrapolation. Results are shown as whole years for whole-year inputs.
Video chapters
- 0:00 — A fictional conversion, real algebra
- 0:14 — Pin both scales at an anchor
- 0:25 — One human year becomes ten fantasy years
- 0:40 — Build the rule from its two parts
- 1:00 — Count years beyond eighteen
- 1:13 — Stretch twelve years by ten
- 1:26 — Add the starting hundred
- 1:37 — Check the straight-line pattern
- 1:53 — Reverse the rule exactly
- 2:09 — Keep the story rule and the math together
Read the full transcript
How do you convert a human age to a vampire age? First, a warning: there is no real-world conversion. This is a playful rule invented for this calculator. We can still understand its mathematics and undo it exactly.
The story begins at an anchor point. A human age of eighteen is assigned a vampire age of one hundred. Picture two rulers pinned together there. The first hundred is the starting value, not something we multiply.
From that point, every extra human year adds ten vampire years. Move one year along the human ruler and ten along the vampire ruler. Move two, and the change is twenty. The rule is linear: the ratio of changes stays ten to one.
Call human age H and vampire age V. Count only the years after the anchor by taking H minus eighteen. Multiply that difference by ten, then add the vampire starting age of one hundred. In symbols: V equals open parenthesis H minus eighteen close parenthesis times ten plus one hundred.
Try H equals thirty. The part beyond eighteen is thirty minus eighteen, or twelve human years. On the paired rulers, that is the span we stretch; multiplying all thirty years would count the anchor incorrectly.
Each of those twelve years corresponds to ten on this fantasy scale. Twelve times ten is one hundred twenty vampire years beyond the anchor. Watch the twelve human segments expand to a hundred twenty vampire segments.
Add back the first hundred: one hundred plus one hundred twenty equals two hundred twenty. So thirty human years correspond to two hundred twenty vampire years under this rule. The arithmetic and both endpoints agree.
A quick graph checks the pattern. The point eighteen, one hundred sits at the anchor. Twenty maps to one hundred twenty. Thirty maps to two hundred twenty. One more human year, thirty-one, maps to two hundred thirty. Every step adds ten; all four points lie on one line.
To go backward, undo the operations in reverse order. Begin with two hundred twenty vampire years. Subtract the starting one hundred to leave one hundred twenty. Divide by ten to recover twelve human years since the anchor. Add eighteen. You get thirty, the starting human age.
The rule is a fictional convention, not a biological or historical fact about vampires. It is anchored at eighteen; extending its line to younger ages is just extrapolation. For this particular story rule, count years after eighteen, multiply by ten, and add one hundred. Reverse it by subtracting one hundred, dividing by ten, then adding eighteen. Thirty maps to two hundred twenty and back.
Sources
- Calculator Academy — the fictional age rule and example
- OpenStax College Algebra — linear functions and slope
- OpenStax College Algebra — inverse functions