The half-life of a radioactive kind of ruthenium is 40 days. If you start with 240 grams of it, how much will be left after 120 days?

30g

Step-by-step explanation:

In this question (t½) of isotope is 40 days, which means that after 40 days half of the sample would have decayed and half would be left as it is.

After 40 days ( first half life) 240 /2 = 120 g decays and 120 g remains left.

After another 40 days ( two half lives or 80 days) 120 /2 = 60 g decays and 60 g remains left .

after three half lives or 120 days, 60/2 = 30g decay and 30 g of the isotope will be left.

step-by-step explanation:

hjkj

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18