Patterns and missing values
Find what is done to each term to get the next, then use the opposite operation to find any unknown.
A worked example
To find the missing number in ▢ + 17 = 45, subtract: 45 − 17 = 28.
The mistake people actually make
Not every pattern adds the same amount each time. Check whether each term is being multiplied instead, as in 3, 12, 48.