The problem I'm having trouble understanding is noted below:
Records show that Oliver is typically 10–30 minutes late for his shift at work. The distribution for the minutes he is late forms a consistent pattern, which can be graphed as the given uniform density curve.
John and Oliver are working a shift that starts at the same time. John always arrives 8 minutes late. What percentage of the time does Oliver arrive within 10 minutes of John's arrival time?
My first step in finding the solution was to multiply the 10 (the minutes within the time that Oliver arrives of John's arrival time) and $\frac{1}{20}$, the height of the density curve. The answer then would be 50%. However, this is not the correct answer. How would you find the correct answer to this problem?