Agroup of scientist study the effect of chemical on various strains of bacteria. strain a started with 12000 cells and decreases at a constant rate of 4000 cells per hour after the chemical was applied. strain b started with 6000 cells and decreased at a constant rate of 3000 cells per hour after the chemical was applied. when will just strains have the same number of cells? explain

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

the first one is x^2+2x+2

the second one is x^2+4

the last one is x^2-4x+8