Math Flash Cards (Free):

Children can build and improve essential math skills in: addition, subtraction, multiplication and division.

Features include:

top and bottom number ranges can be edited
number ranges: 0 to 50 for addition and subtraction
number ranges: 0 to 20 for multiplication and division
option to select two math operations together

adjustable countdown timer for test-like conditions

option to allow cards in order (for quicker memorization) or random
option to show correct answer if wrong
option to allow three tries
option to repeated missed cards for review at the end

friendly and encouraging voice
scores list to review improvement

This app is free but is support by ads.
A paid ad-free version is available.