To calculate the fraction of days starting with 'S' (Saturday and Sunday) or 'T' (Tuesday and Thursday) of the week, you need to consider that there are seven days in a week. Out of these seven days, there are four days that start with 'S' or 'T.' Let's list them:

1. Saturday
2. Sunday
3. Tuesday
4. Thursday

Now, let's calculate the fraction:

Fraction of days starting with 'S' or 'T' = (Number of days starting with 'S' or 'T') / (Total number of days in a week)

Fraction of days starting with 'S' or 'T' = 4 / 7 ≈ 0.5714

So, the fraction of days starting with 'S' or 'T' of the week is approximately 0.5714 or 57.14%