The average of 7 numbers is 60. The average of the first three numbers is 50, while the average of the last three is 70. What must be the remaining number ?

The sum of all the seven numbers = 60 * 7 = 420
The sum of the first three = 50 * 3 = 150
The sum of the last three = 70 * 3 = 210
Remaining Number = 420 – (210 + 150) = 60