Question

When two waves are in sync with each other and occupy the same place at the same time, how is the resulting wave determined?

by averaging the wavelengths of the two waves
by dividing the frequencies of the two waves
by multiplying the velocities of the two waves
by adding the amplitude of the two waves

Answer 1

By adding the amplitudes (superposition principle). The resulting displacement at each point and time is y_total = y1 + y2 (in-phase gives constructive interference; opposite phase gives subtraction/destructive).