In a certain city each of 28 primary schools is represented by a colored flag. Each flag consists of either a single color or a pair of two different colors. If each school has a different flag, what is the minimum number of colors needed for the flags. (Assume that the order of colors in a pair on a flag does not matter.)
Options
A) 7  B) 9  C) 8  D) 10  E) 5
A.7:   if we have 7 colors we can choose pairs in 7C2 ways = 21 and single color flags are 7. Therefore total number of flags = 28.   7NS 7.
<result>A</result>
In a certain city each of 28 primary schools is represented by a colored flag. Each flag consists of either a single color or a pair of two different colors. If each school has a different flag, what is the minimum number of colors needed for the flags. (Assume that the order of colors in a pair on a flag does not matter.)