At the same time of day, a 6-foot-tall person casts a 4-foot shadow and a tree casts a 30-foot shadow. How tall is the tree?
Show answer & explanation
Answer: C
20 feet: 20 sets up the ratio upside down (30 × 4/6); taller objects cast longer shadows, so the tree must be taller than its shadow here.
32 feet: 32 adds the 2-foot difference between the person's height and shadow; the relationship is multiplicative, not additive.
45 feet: Correct. Height/shadow is the same for both: 6/4 = h/30, so h = 30 × 1.5 = 45 feet.
180 feet: 180 multiplies the person's height by the tree's shadow without dividing by the person's shadow.
Objects and their shadows at the same time form similar triangles: height₁/shadow₁ = height₂/shadow₂.