MathBeasts Demo

Spot the beast behind a math error, fix it, and see why the fix works.

Interactive demo · sample dataVisit BeastScholar

River Valley Beast Campus · BeastCampus · MathBeastsIllustrative school-branded header. Not a live school site.

Sample student work

1/3 + 1/4
= (1 + 1)/(3 + 4)
= 2/7

1. Identify the beast
2. Fix the answer
3. Understand why

Which beast caused this error?

Complete MathBeasts catalog

45 beasts in five families

From the BeastScholar catalog. Track tags are proposed instructional mappings, not claims about any college’s requirements. One free sample per family; all others are locked to school portal access. Beasts without approved BeastScholar artwork show their symbol. The guided walkthrough above (Denominator Danny, Distributor Dee, One-Side Wes) is a short demo, not catalog access.

Showing 45 of 45

$Place-Value Pip artwork$
Place-Value PipFree sample
Whole numbers & place value · Foundations
Lines numbers up by their left-hand digits instead of by place value.
Play free sample
$Rounding Rogue artwork$
Rounding RogueLocked · School access
Estimation & rounding · Foundations
Rounds intermediate results, so the error compounds before the final answer.
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$Sign-Switch Sam artwork$
Sign-Switch SamLocked · School access
Signed numbers · Foundations
Treats subtracting a negative as subtracting, and mis-signs products of negatives.
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$Denominator Danny artwork$
Denominator DannyLocked · School access
Fractions · Foundations
Adds the denominators when adding fractions with unlike denominators.
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$Decimal Drift artwork$
Decimal DriftLocked · School access
Decimals · Foundations
Places the decimal point in a product by copying one factor's places.
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$Ratio Ripper artwork$
Ratio RipperLocked · School access
Ratios & proportions · Foundations
Reverses which quantity each part of a ratio describes.
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$Percent Phantom artwork$
Percent PhantomLocked · School access
Percentages · Foundations
Converts a percent to a decimal by moving the point one place instead of two.
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$Order-of-Ops Ollie artwork$
Order-of-Ops OllieLocked · School access
Order of operations · Foundations
Works strictly left to right, ignoring grouping and operation precedence.
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$Like-Term Larry artwork$
Like-Term LarryFree sample
Like terms · Algebra
Combines terms with different powers as if they were like terms.
Play free sample
$Distributor Dee artwork$
Distributor DeeLocked · School access
Distribution · Algebra
Multiplies only the first term inside the parentheses.
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$One-Side Wes artwork$
One-Side WesLocked · School access
Equality & linear equations · Algebra
Applies an operation to only one side of an equation.
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$Flip-Flop Fiona artwork$
Flip-Flop FionaLocked · School access
Inequalities · Algebra
Keeps the inequality direction after multiplying or dividing by a negative.
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$Exponent Ezra artwork$
Exponent EzraLocked · School access
Exponents · Algebra
Adds exponents when raising a power to a power.
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$Binomial Bruno artwork$
Binomial BrunoLocked · School access
Polynomials & factoring · Algebra
Squares a sum term by term, dropping the middle term.
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$Canceling Carl artwork$
Canceling CarlLocked · School access
Rational expressions · Algebra
Cancels a term that is added, rather than a common factor.
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$Root-Split Rhea artwork$
Root-Split RheaLocked · School access
Radicals · Algebra
Splits a square root across a sum.
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$Swap-Coord Cora artwork$
Swap-Coord CoraFree sample
Coordinates · Functions & Graphs
Plots (x, y) with the coordinates swapped.
Play free sample
$Rise-Run Rudy artwork$
Rise-Run RudyLocked · School access
Slope · Functions & Graphs
Computes slope as run over rise.
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$Intercept Iggy artwork$
Intercept IggyLocked · School access
Intercepts · Functions & Graphs
Finds the x-intercept by setting x = 0.
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$Notation Ned artwork$
Notation NedLocked · School access
Functions · Functions & Graphs
Reads f(x + 2) as f(x) + 2.
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$Half-Solve Sully artwork$
Half-Solve SullyLocked · School access
Systems of equations · Functions & Graphs
Reports one variable's value as the whole solution of a system.
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$Root-Drop Quill artwork$
Root-Drop QuillLocked · School access
Quadratics · Functions & Graphs
Keeps only the positive root when solving a squared equation.
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$Linear Lyle artwork$
Linear LyleLocked · School access
Exponential growth · Functions & Graphs
Treats a constant percent growth rate as adding a constant amount.
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$Log Lars artwork$
Log LarsLocked · School access
Logarithms · Functions & Graphs
Treats the log of a sum as the sum of logs.
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$Unit Ursula artwork$
Unit UrsulaFree sample
Units & conversions · Quantitative Reasoning
Combines measurements in different units without converting.
Play free sample
$Rate Reggie artwork$
Rate ReggieLocked · School access
Rates · Quantitative Reasoning
Averages two speeds directly when the times differ.
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$Rate-Period Petra artwork$
Rate-Period PetraLocked · School access
Financial math · Quantitative Reasoning
Applies an annual interest rate to a single monthly period.
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$Markdown Mort artwork$
Markdown MortLocked · School access
Percent change · Quantitative Reasoning
Assumes a percent increase and the same percent decrease cancel.
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$Area-Scale Archie artwork$
Area-Scale ArchieLocked · School access
Geometry & measurement · Quantitative Reasoning
Thinks scaling lengths by k scales area by k.
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$Trendline Trixie artwork$
Trendline TrixieLocked · School access
Modeling · Quantitative Reasoning
Extends a model far beyond the data it was built from.
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$Magnitude Max artwork$
Magnitude MaxLocked · School access
Reasonableness · Quantitative Reasoning
Accepts an answer without noticing it is the wrong size.
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$Axis Axel artwork$
Axis AxelFree sample
Interpreting graphs · Statistics & Probability
Reads bar heights on a truncated axis as proportional to the values.
Play free sample
$Median Mabel artwork$
Median MabelLocked · School access
Center · Statistics & Probability
Takes the middle value of an unsorted list as the median.
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$Spread Spencer artwork$
Spread SpencerLocked · School access
Spread · Statistics & Probability
Thinks bigger values mean more spread.
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$Gambler Gus artwork$
Gambler GusLocked · School access
Probability · Statistics & Probability
Believes independent outcomes are 'due' after a streak.
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$Converse Connie artwork$
Converse ConnieLocked · School access
Conditional probability · Statistics & Probability
Treats P(A | B) as if it were P(B | A).
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$Volunteer Vera artwork$
Volunteer VeraLocked · School access
Sampling & bias · Statistics & Probability
Generalizes from a voluntary-response sample to a whole population.
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$Causal Cal artwork$
Causal CalLocked · School access
Association & causation · Statistics & Probability
Concludes causation from an observed correlation.
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$P-Value Penelope artwork$
P-Value PenelopeLocked · School access
Statistical inference · Statistics & Probability
Reads a p-value as the probability the null hypothesis is true.
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$Product Pippa artwork$
Product PippaLocked · School access
Fraction multiplication · Foundations
Keeps a common denominator when multiplying fractions, as if multiplication were addition.
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$Reciprocal Rex artwork$
Reciprocal RexLocked · School access
Fraction division · Foundations
Inverts the dividend instead of the divisor when dividing fractions.
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$Zero-Product Zora artwork$
Zero-Product ZoraLocked · School access
Factored equations · Algebra
Divides a factored equation by a variable expression and loses the case where that factor is zero.
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$Domain Dora artwork$
Domain DoraLocked · School access
Real function domains · Functions & Graphs
Assumes every real input is valid without checking denominators, roots and logarithms.
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$Overlap Orla artwork$
Overlap OrlaLocked · School access
Overlapping events · Statistics & Probability
Adds overlapping event probabilities without subtracting the outcomes counted twice.
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$Weightless Walt artwork$
Weightless WaltLocked · School access
Weighted means · Statistics & Probability
Averages group means equally even when the groups contain different numbers of observations.
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