Start with mass per second, not with memorised symbols Write mass entering per second equals mass leaving per second. Only then reduce the statement to a1 v1 rho1 = a2 v2 rho2 and to a1 v1 = a2 v2 for incompressible flow.

Read the area change before touching the calculator If area shrinks, speed must rise. If area widens, speed must fall. This proportional check solves many options without full arithmetic.

Use continuity inside real flow pictures Rivers in hilly regions, narrow pipe throats, and water streams from a tap are all continuity situations before they are anything else.

Keep incompressibility explicit The reduction to av = constant works only after rho is taken the same at both sections. If density changes, the full mass-flow form must be kept.

Do not confuse area with radius or diameter Area depends on radius squared, so if the pipe radius changes, convert it into cross-sectional area before using the continuity relation.