Chika Ofili, a 12-year-old Nigerian boy based in the UK received recognition for discovering a new way to test the divisibility of a number by 7.
This test is named after him as it is called as Chika’s Test.
The test is done by taking the last digit of a number and multiplying it by 5 and adding the product to the remaining number. If the resulting number is divisible by 7, then the original number is divisible by 7.
However, if the resulting number is still big and hard to tell if it is divisible by 7, the steps can be repeated until an obvious 2-digit number come out.
Below is the example or proof of the test.
According to the test, if the steps were done repeatedly on a certain number that’s divisible by 7, the end result is either 7 or 49.