In a right triangle the two legs are in the ratio 1 : 2. If θ is the smaller acute angle, then sinθ·cosθ equals:

Take the legs as 1 and 2, so the hypotenuse is √(1 + 4) = √5. The smaller angle faces the shorter leg, giving sinθ = 1/√5 and cosθ = 2/√5, so the product is 2/5 = 0.4 (here θ ≈ 26.57°). The distractors are the pieces of that calculation: 1/5 is si$n^2$θ, 4/5 is co$s^2$θ and 2/√5 is cosθ on its own.