Free practice · boolean · easy
Practice
Avoid an unweighted average of averages
Two group averages can always be averaged directly even when the groups have different sizes.
Combination math map
Use equal weights only when the observations are equally weighted
Simple mean
NumeratorSum of values
DenominatorEqual count
Weighted mean
NumeratorΣ value × weight
DenominatorΣ weights
Allocation
ShareWhole × part/total
CheckParts + remainder
Weighted means preserve quantities, proportional allocations preserve shares, and a remainder check reconnects every part to the original whole.