To answer this question, the sum of 3 numbers needs to be subtracted from the sum of all 4 numbers. You can find the sum of 3 numbers by multiplying the given average by 3.
Now you can subtract this total from the total of all four numbers.
The fourth number is 351!
To find the sum of the three numbers that average to 293, multiply 293 by 3.
You multiply by 3 because when you originally find the average of 3 numbers, you divide the sum of the numbers by 3.
average = sum of numbers / # of numbers
If you subtract 879 from the sum of all 4 numbers (1230), then you know the fourth number.
The fourth number is 351.