What you are actually practicing
A number is odd or even based on its last digit alone. 4,317 is odd because it ends in 7; the thousands, hundreds and tens are irrelevant. That single fact turns a slow check into a glance.
This game asks you to classify a short list and report a count — a combination of two skills that are easy alone and error-prone together.
How the game works
You are shown a short list of numbers and four counts. Pick how many are odd. A wrong pick reveals the answer immediately.
Easy uses four numbers under twenty. Medium uses five numbers under a hundred. Hard uses five numbers up to three digits, where the last digit is easier to lose.
The relationship worth knowing
Odd last digits: 1, 3, 5, 7, 9. Everything else is even — including numbers ending in 0.
The rest of the number does not matter: 1,000,003 is odd; 1,000,030 is even.
Strategies that actually raise your score
Look only at the final digit. Reading whole numbers wastes the clock. Glance at the right-hand edge of each number and move on.
Tally as you go, do not recount. Mark each odd number you see by holding a running total. Re-scanning the list from the start is where double-counts appear.
Use the total as a bound. With five numbers the answer cannot exceed five, and cannot be zero if any number visibly ends in an odd digit. Both bounds often remove two options.
Check the complement when unsure. Counting the evens and subtracting from the list length is sometimes faster, and it is a free cross-check on your first count.