How to solve these question in detailed steps From long-term observation, it is known that the waiting-time for non-ambu

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How to solve these question in detailed steps
From long-term observation, it is known that the waiting-time
for non-ambulance adult arrivals in a hospital's A&E has an
approximately Normal distribution with mean of 120 minutes and a
standard deviation of 50 minutes.
a) What proportion of arrivals wait between 60 minutes and 180
minutes?
b) The hospital has a target that 99% of arrivals will be seen
within 4 hours (240 minutes). What proportion are seen within that
time and is it meeting the target?
c) Management want to set a new target for 90% of arrivals. What
time would you suggest?