Picking variable
Pick variables the represent numbers
Age Questions
Now and Later; pick the variable for now
Two travelers opposite direction
Sum of speeds:
Towards each other- shrinking; Away: expanding
Two travelers moving in same direction (big-small)
Difference of speeds; faster in front: expanding; faster behind: shrinkingq
Shrinking/expanding
one equation for gap; can add gaps if gaps are the same
A
RT
Rab=
Ra+Rb
Solute/
Solute+Solvent
Venn
only! regions add
Sum of sequences
n(n+1)/2 any evenly spaced pair of numbers; have to find the number of pairs