The goal of the game is to provide the missing digits in the arithmetic expressions. There are always at most two missing digits, and one is always to the right from another. The digits are filled by tapping on or sliding over the two controls containing digits from 0 to 9 at the left and right edges of the screen or game window. Left control drives the left missing digit and right control drives the right one. If only one digit is missing in the expression, then it can be chosen by either of the controls.

On the mobile devices with the touch screens, the digit controls are most easily operated by the thumbs, hence the name of the game.

If the keyboard is present, then the regular numeric keys control the left digit and the keypad keys, if the keypad is present, control the right digit. Both sets of the numeric keys control a single missing digit. Mouse can also be used to click on both the left and the right number controls on the screen.

Each problem is given a limited time to be solved, as indicated by the progress bar at the bottom. The correct solution is auto-recognized one second after the numbers were last chosen. If the solution is provided, then the expression will “blow up”.

To force immediate acceptance and not wait for a second, tap on the problem area. If the expression won’t blow up this means that your solution is wrong.

If the correct solution is not provided during the allocated time, the correct solution will be shown for 3 seconds. Tap on the problem area to force generation the new problem without waiting for 3 seconds.

To force regeneration of the problem, tap on the “fast forward” control, to the right of the “play/pause” button Each problem type has its score depending on the complexity.

If the keyboard is present, then one can force immediate acceptance or skip viewing the correct answer by pressing “spacebar”. To fast forward to the next problem, press Escape of Tab key.

The total score is displayed in the top middle of the screen.

The number of seconds allocated for solving a problem is 5 plus the problem’s score.

SETTINGS

The Settings screen always choosing the types of problems and configuring them. There are to two settings, applied to all problems.

a. Calculation vs missing number problems, i.e. A+B=_ vs A+_=C.
b. Fractions of the negative terms, the extreme examples would be A-B vs -A-(-B), where A and B are always positive.

Problems of five types are available. A problem type is added to the game by checking the checkbox next to it.

1. Simple single step addition, subtraction, multiplication or division. You can choose which of the four operations are included. In the case if additional, each term will be less than 100, and if negative terms are not allowed, then the difference of a subtraction will always be positive. Multiplication and division terms go up to 12.

2. Long operations: addition, subtraction and multiplication. All terms and the result are guaranteed to be positive. The largest term is always more than 100, and the second multiplication term is one digit.

3. Nested brackets: expression like A+(B-(C-D)). It is possible to choose the number of nesting, between 1 and 4. The terms are always one-digit.

4. Multistep expressions: up to two multiplication or divisions, connected by an addition or a subtraction, e.g. AxB – C/D, or A + CxD.

5. Fractions: addition, subtraction, multiplication and division of proper fractions. You can save, edit and delete your game configurations, using the controls on the left half of the Settings screen.

Two configurations are provided by default and cannot be edited or deleted.

Simple configuration only has the one step problems, containing all operations.

Full configuration has all problems, with default settings for the fraction of the missing number problems (33%) and negative terms (25%).

This game is offered as a MONTHLY SUBSCRIPTION, without which only additions and subtractions <100 are supported.