Divisibility and Digit Sums

In this video, Mr. J explains the divisibility rule for 15, which states that a number is divisible by 15 if it is divisible by both 3 and 5. He demonstrates this rule through four examples: 1470, 1335, 8951800, and 1008525. For each example, he calculates the sum of the digits to check divisibility by 3 and examines the last digit to check divisibility by 5. The video concludes with a summary of the rule and its application.

What is the main purpose of checking for divisibility?

• To find the largest number

• To determine if a number can be divided without a remainder

• To find the smallest number

• To check if a number is even

Which two numbers must a number be divisible by to also be divisible by 15?

• 3 and 5

• 2 and 5

• 5 and 6

• 3 and 4

How do you determine if a number is divisible by 3?

• Check if it ends in 0 or 5

• Check if the sum of its digits is divisible by 3

• Check if it is an even number

• Check if it is a prime number

What is the sum of the digits of 1470?

• 10

• 12

• 14

• 16

Why is 1470 divisible by 5?

• It is an even number

• It is a prime number

• It is less than 1000

• It ends in a 0

What is the sum of the digits of 1335?

• 10

• 12

• 14

• 16

Why is 1335 divisible by 5?

• It is less than 1000

• It is an even number

• It is a prime number

• It ends in a 5

What is the sum of the digits of 8,951,800?

• 34

• 33

• 32

• 31

Why is 8,951,800 not divisible by 15?

• It is not divisible by 3

• It is not divisible by 4

• It is not divisible by 5

• It is not divisible by 2

What is the sum of the digits of 1,008,525?

• 21

• 20

• 22

• 19