Distance, Rate, and Time
Formula: d = r × t (distance = rate × time). Rearrange: r = d/t and t = d/r.
Average speed for a whole trip = total distance ÷ total time. Do not average the speeds directly — that only works if equal time is spent at each speed.
Two-object problems: - Objects moving toward each other: add their speeds to find closing rate. - Objects moving same direction: subtract speeds to find closing rate.
Upstream/downstream: Boat speed downstream = boat speed + current. Upstream = boat speed − current.