GMAT Prep

[rosh26]

Why is A sufficient? Can someone pelase work out. Thanks.

[sethids]

The only information available from the question stem is the number of people but that too is a variable n.

Stmt1: Average height of n/3 tallest people is 6 feet 2.5 inches = 74.5 inches.
Combined height (sum of the height of all the tallest n/3 people) = (n/3) * 74.5

the rest of the group is 2n/3 and the average height is 5 ft 10 inches = 70 inches.
Combined height = (2n/3) * 70

Combined height of the entire group
= (n/3) * 74.5 + (2n/3) * 70
= (n/3) * (74.5 + 140)
= (n/3) * (214.5)

Mean height is this total divided by n i.e.
((n/3) * (214.5))/n
= 214.5/3 = 71.5 inches.

Sufficient.

Stmt2: Total height of the group is given but we don't know the value of n. Insufficient.

Hence A.