Final answer:
The symbol for a t-score typically is just represented as 't' and not by letters. In this case, additional instructional context is required to determine the correct symbol. T-scores follow a Student's t-distribution and are used in statistical analysis.
Step-by-step explanation:
The student has mentioned a t-score of 20 for scale 7 and is asking about the symbol for the t-score. The provided choices do not directly relate to the typical notation for a t-score, as t-scores are usually just referred to as 't'. However, if this is related to a specific grading or scoring system that uses letters to indicate t-score ranges, additional context from the educational material or instructions would be necessary to determine the correct symbol.
T-scores follow a Student's t-distribution with degrees of freedom based on the sample size minus one (df = n - 1). They are used to determine how far a sample mean is from the population mean in units of standard error, especially when the sample size is small and the population standard deviation is unknown. T-scores have a mean of zero and are sometimes used instead of z-scores, which assume a standard normal distribution with a mean of 0 and a standard deviation of 1.
If the t-score is being used in the context of hypothesis testing or confidence intervals, the calculation would depend on the sample mean, sample size, and sample standard deviation.