A school has 20 classrooms. One
fourth of the classrooms are
for kindergarten and first
grade. Twice as many are
for second and third grade.
The rest are for fourth and
fifth grade. What percent
of the classrooms are for 45
or 5th graders

One forth of 20 is 5, so there are 5 kindergarten and first grade classrooms.

5 x 2 is 10 so there are 10 second and third grade classrooms.

10 + 5 is 15.

20 - 15 is 5.

There are 5 forth and fifth grade classes.

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