1. Divisibility and Mental Math
LESSON 4-1
Additional Examples
Is the first number divisible by the second? Use mental math.
a. 46 by 3
b. 63 by 7
Think Since 3  15 = 45
and 3  16 = 48, 46 is not
divisible by 3.
Think Since 7  9 = 63,
63 is divisible by 7.

2. Divisibility and Mental Math
LESSON 4-1
Additional Examples
Test each number for divisibility by 2, 3, 5, or 10.
a. 580
b. 3,042
580 ends with a 0.
So it is divisible
by 2, 5, and 10.
3,042 ends with a 2.
So, it is divisible by 2,
but not by 5 or 10.
The sum of its digits
is 9, which is divisible
by 3. So, it is divisible
by 3.

3. Divisibility and Mental Math
LESSON 4-1
Additional Examples
A baker sells muffins in boxes that contain exactly 9 muffins each. Can the baker place 576 muffins in boxes of 9 with none left over?
If 576 is divisible by 9, then there will be no muffins left over.
= 18 Find the sum of the digits in 576.
18 ÷ 9 = 2 The sum is divisible by 9.
So, 576 is divisible by 9. There will be no muffins left over.