Extrapolate that means to plot existing data and predict or draw a curve that for a range outside the existing data.
Interpolate comes from the Latin interpolatus (1612).
Interpolate means to add things in. Like when you "guesstimate" a rough answer to a math question...this is interpolation. "Edward had to interpolate the approximate arrival of the airplane." "Harvy...
"If you interpolate from the values around it, you can find the value of X in this equation.""To interpolate the value, compare it to known values."