How much of a radioactive kind of iodine will be left after 42 hours if the half-life is 21 hours and you start with 120 grams?

30 grams

Step-by-step explanation:

If the half life is 21 hours, that means after 21 hours, the initial amount will decrease to half.

So, since we started with 120 grams, it will be at 60 grams after 21 hours.

After another 21 hours have passed (after a total of 42 hours), the amount of 60 grams will split in half again to 30 grams.

So, after 42 hours, there will be 30 grams left of the radioactive iodine

infinitely many solutions

step-by-step explanation:

we have been given the equation;

2(2x + 3) = -4 + 2(2x + 5)

we need to determine the value of x.

2(2x + 3), we expand this expression to obtain 4x + 6

similarly 2(2x + 5) will become 4x + 10

now we have;

4x + 6 = -4 + 4x + 10

4x + 6 = 4x + 10 - 4

4x + 6 = 4x + 6

the expression on the left hand side is identical to the one on the right hand side. therefore, we are looking at just a single straight line whose equation is;

y = 4x + 6

consequently, we shall have infinitely many solutions