The average of 5 numbers, arranged in a row, is 309. The average of the first two of these numbers is 431 and the average of the last two of these numbers is 231.5. What is the value of the number at the center of the row?

321 52 108 220

220

Sum of 5 numbers = 5 x 309 = 1545 Sum of 1st two numbers = 2 x 431 = 862 Sum of last two numbers = 2 x 231.5 = 463 Center number = 1545 - 862 - 463 = 220