The fraction of the surface area of a pond covered by algae cells double every week. Today, the pond surface is fully covered with algae. This situation can be modelled C= (1/2)^t, where C is the fraction of the surface area covered by algae t weeks ago. When was 25% of the pond covered?

300

step-by-step explanation:

28-600w < 300

28-600w > 300

600-28w < 300

600-28w > 300

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

3

step-by-step explanation: