Divisibility Rules and Methods

The video explores various card tricks to demonstrate divisibility rules for numbers like 3, 9, and 7. It includes mathematical proofs and a unique skill of a friend named Norrie. The video concludes with a promotion for Brilliant's educational platform.

What was the outcome of the bet between the narrator and Brady regarding the number's divisibility by 9?

• The number was not divisible by 9.

• The number was divisible by 9.

• The number was odd.

• The number was prime.

What is the significance of the cross sum in determining divisibility by 3?

• It determines if a number is prime.

• It helps in arranging cards in order.

• If the cross sum is divisible by 3, the number is divisible by 3.

• It is used to find the largest digit in a number.

Which of the following is a rule for checking divisibility by 4?

• Check if the last digit is 4.

• Check if the number ends in 0.

• Check if the last two digits form a number divisible by 4.

• Check if the sum of all digits is 4.

What is the rule for checking divisibility by 11?

• Check if the number is even.

• Check if the sum of all digits is 11.

• Check if the alternating sum of digits is a multiple of 11.

• Check if the number ends in 11.

How does Norrie determine if a number is a multiple of 7?

• He checks if the number ends in 7.

• He divides the number by 7.

• He feels a sense of warmth towards the number.

• He uses a calculator.

What is the first step in the general divisibility method for numbers ending in 1, 3, 7, or 9?

• Subtract 1 from the number.

• Divide the number by 10.

• Multiply the number to make it end in 9.

• Add 1 to the number.

What is the purpose of creating a 'divvy number' in the general divisibility method?

• To find the largest digit in the number.

• To simplify the number.

• To convert the number to binary.

• To check if the original number is divisible by the target number.

Which numbers can the general divisibility method be applied to?

• Numbers ending in 2, 4, 6, 8

• Numbers ending in 5

• Numbers ending in 1, 3, 7, 9

• Numbers ending in 0, 2, 4, 6, 8

What is the final step in the general divisibility method?

• Divide the number by 10.

• Add 1 to the number.

• Multiply the number by 10.

• Subtract 1 from the number.

What is the main challenge in the general divisibility method?

• Ensuring the number ends in 9.

• Finding the largest digit in the number.

• Finding a number that ends in 0.

• Making the number even.