Integer Add Subtract Vault

About Integer Add Subtract Vault

Integer Add Subtract Vault is the first of our Logic Masters games and it targets the single most reliable place where a confident arithmetic student suddenly starts getting things wrong. The cause is not difficulty in any ordinary sense — it is that two entirely different minus signs are in play at once. One means subtract, an instruction to do something; the other means negative, a property of the number itself. Written down they look identical, and an expression like 3 minus negative 5 contains both. Children cope by inventing rules, and the rules they invent tend to work on the examples they were shown and fail elsewhere: two minuses make a plus is repeated confidently by students who then apply it to negative three plus negative four and produce seven. This game therefore uses all four combinations deliberately — adding a negative, subtracting a positive, subtracting a negative, and starting from a negative — rather than the two that appear most often in textbooks. A pupil who meets only the common cases builds exactly the fragile rules described above. The wrong answers are the sign errors themselves: the right magnitude with the wrong sign, and the result of treating a double negative as a subtraction, so a slip in reasoning is caught rather than accidentally landing on the right answer. Subtracting a negative, the hardest case, is held back until the third level. Free, no sign-up, no advertising to children, progress kept on the device.