The Berlin Numeracy Test.  A 4-question validated measure of numerical literacy.

See Cokely, E. T., Galesic, M., Ghazal, S., Schulz, E., &
Garcia-Retamero, R. (2012). Measuring risk literacy:
The Berlin Numeracy Test. Judgment and Decision
Making, 7, 25–47.

Parameters control both whether the test is administered in an
adaptive manner, and if you use the multiple-choice version versus the
free-response one (answers to which might need hand-verification)
