Python:

 # a1 = 1.12,1.25,3.1
# b1 = 2,3,4,5
# print(2,2,4) # результат
a1 = [1.12, 1.25, 3.1]
b1 = [2, 3, 4, 5]
def get_figure(num, seq):
    diff = [i - num for i in seq]
    term = [i for i in diff if i >= 0]
    ind_ = diff.index(min(term))
    return seq[ind_]
print([get_figure(i, b1) for i in a1])