Final answer:
The correct mathematical expression for a number increased by eight twenty-sevenths of itself is 'x + (8/27)x', which is option C.
Step-by-step explanation:
The student has asked about a mathematical expression involving a number increased by a fraction of itself. The correct expression should represent the original number plus the additional fraction of that number. To represent a number increased by eight twenty-sevenths of itself, we would take the number, which we can denote as 'x', and then add to it eight twenty-sevenths of 'x'. Mathematically, this is shown as:
x + (8/27)x
Therefore, the correct option from the given choices is:
A step-by-step explanation includes recognizing that the phrase 'increased by' indicates addition, while 'eight twenty-sevenths of itself' means to multiply the number 'x' by 8/27 and then add that product to the original number 'x'.