From the stem, what we are given is:
Courier travels in three non-stop legs, consecutively. Let the distances travelled and time taken in legs 1, 2 and 3 respectively be d1, d2 and d3 and t1, t2 and t3
Average speed in leg 1, 2 and 3 is 40km/hr, 60km/hr and 80 km/hr
Thus,
d1/t1 = 40 ==> d1 = 40*t1 ==> t1 = 40/d1
d2/t2 = 60 ==> d2 = 60*t2 ==> t2 = 60/d2
d3/t3 = 80 ==> d3 = 80*t3 ==> t3 = 80/d3
We need to find the overall average speed of the entire journey,
(d1+d2+d3)/(t1+t2+t3) = ?
Lets go to our statements:
Statement 1: t1:t2:t3 = 3:2:1
THus, we know,
t1/t2 = 3/2 ==> t1 = (3/2)*t2
t2/t3 = 2/1 ==> t3 = t2/2
Now, we can express the above required overall average speed in just one variable t2
(40*(3/2)*t2 + 60*t2 + 80*t2/2)/((3/2)*t2 +t2 +t2/2)
We do not need to go ahead and solve this entirely. We just need to know if this statement is enough to get there. Clearly it is. So we can eliminate B, C and E
Statement 2: d1:d2:d3 = 3:3:2
Thus,
d1 = d2,
d2/d3 = 3/2 ==> d3 = 2/3*(d2)
Now, we have the relations of d1 and t1, d2 and t2, d3 and t3, thus, we can express the overall average speed in a single variable d2 as below:
{(d2+d2+(2/3)*d2)/[(40/d2)+(60/d2)+(80/((2/3)*d2))]}
Thus, we can easily calculate this ratio. Thus, this statement is also enough by itself. We can eliminate A
(D) is the correct answer choice