Notes of multiplying decimals

Multiply the numbers just as if they were whole numbers.

Line up the numbers on the right - do not align the decimal points.

Starting on the right, multiply each digit in the top number by each digit in the bottom number, just as with whole numbers.

Add the products.

Step-by-step explanation:

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional