3 legs of journey
First leg, avg speed = 40, distance = d1, time = t1
Second leg, avg speed = 60, distance = d2, time = t2
Third leg, avg speed = 80, distance = d3, time = t3
Total avg speed for trip = total distance/ total time = (d1+d2+d3)/(t1+t2+t3)
Statement A : t1:t2:t3 = 3:2:1 => t1 = 3x, t2 = 2x, t3 = x (let x be a constant)
D = S x T => d1 = 40x t1 = 60 x 3x = 120x
d2 = 60 x t2 = 60 x 2x = 120x
d3 = 80 x t3 = 80 x x = 80x
Avg speed = (120x + 120x +80x)/(3x+2x+x). X cancels out so avg speed can be calculated. Statement A alone is sufficient
Statement B : d1:d2:d3 = 3:3:2 =>d1 =3x, d2 =3x, d3 =2x (let x be a constant)
D = S x T = > T = D/S
T1 = d1/s1 = 3x / 40, similarly t2 = 3x / 60, t3 = 2x/80
Average speed = (d1+d2+d3)/(t1+t2+t3) = (3x+3x+2x)/(3x/40+3x/60+2x/80) X gets cancelled out and average speed can be calculated.
Statement B alone is sufficient
Each statement alone is sufficient. Answer D