A local bank that has 20 branches uses a two-digit code to represent each of its branches. The same integer can be used for both digits of a code, and a pair of two-digit numbers that are the reverse of each other (such as 17 and 71) are considered as two separate codes. What is the fewest number of different integers required for the 20 codes?  Options.
A) 3 B) 4 C) 7 D) 6 E) 5
Pick any two integer.   Integers: 12   Code: 11, 12, 21, 22 = 4 Codes   Add one more integer: 3   13, 31, 33, 23, 32 = 5 Codes   Add one more integer: 4   44, 14, 41, 24, 42, 34, 43 = 7 Codes   Add one more integer: 5   55, 15, 51, 25, 52, 35, 53,54,45 = 9 Codes   Total = 25 Codes. Enough.   Answer: 5
<result>E</result>
A local bank that has 20 branches uses a two-digit code to represent each of its branches. The same integer can be used for both digits of a code, and a pair of two-digit numbers that are the reverse of each other (such as 17 and 71) are considered as two separate codes. What is the fewest number of different integers required for the 20 codes?