If a and b are mutually exclusive, the maximum value of the sum
S=P(a) + P(b)
cannot exceed 1.
Since 0.48+0.62=1.1 >1,
a and b cannot be mutually exclusive.
If it is still not clear, sketch a Venn diagram to convince yourself that it is not possible to draw a and b such that P(a)+P(b)>1 while a and b are mutually exclusive.