Chika’s mathematic’s teacher, Miss Mary Ellis who is also the head of the mathematics department at Westminster Under School said the 12-year-old discovered the new formula while solving a holiday assignment.
The book had several divisibility tests which are used to quickly work out whether a number is exactly divisible by either 2, 3, 4, 5, 6, 7, 8 or 9 before you start dividing, but had no easy or memorable test listed for checking divisibility by 7.
Chika however solved this and also had an algebraic proof to back it up. His new formula involves taking the last digit of any whole number, multiplying it by 5 and then adding it to the remaining part of the number to get a new number. If this new number is divisible by 7, then the original number is divisible by 7