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St Francis de SalesCatholic Junior School

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16/10/2018: Divisibility Rules (& Tricks!)

Divisibility Rules:


Today, our class started to look at the rules of divisibility and how to use reasoning to prove/disprove theories. We already knew some of the easier rules: a number is divisible by 2 if it is even; a number is divisible by 5 if it ends in a 0 or 5 and a number is divisible by 10 if it ends in 0. So, we moved onto 3s, 4s, 6,s and 9s. To do this, we also learnt how to find a digit sum and how to find a digit root! It blew our minds! We needed to use these tricks to find the divisibility rules for our numbers. 


After that, we tackled some missing number division problems and had to predict whether or not they would have a remainder, based on our divisibility rules. On top of that, we had to try our luck at sir's 'sometimes, always or never' problem:


'A two-digit number, when added to its reverse, will always equal a number that is equally divisible by 11!'


We found out that this is ALWAYS true and have been given a home-task to find out what happens when you add a three-digit number to its reverse!


Rachel, Daniel, Simra & Leo