Urgent s2 Question help ...

Im currently doing this question and I done everything up until the end bit where the mark scheme ended up taking away 1 from the answer when integrating. I used to the intervals of 1.5 and 2.5 and integrated correctly...
But at the end they ended up taking away 1 I don't understand, can someone explain please...

thanks in advance guys

where's the question?

http://www.examsolutions.net/a-level-maths-papers/Edexcel/Statistics/Statistics-S2/2012-June/paper.php#Q5

Q5

When you intergrated you found the area between the two points, hence the probability that the customers time will NOT differ from the mean by at least 1.

To find out the probability that the time DOES differ you do 1- whatever the value is because the sum of all probabilities =1

Hope this helped!