The half-life for such a substance is the time 
required to have the amount (in grams 
) at time (in seconds 
), 
, decay to half the starting amount 
. In other words, for krypton-91, after 10 seconds we would have 
. We can use this information to solve for 
, then plug in various values of to find the amount of krypton-91 that's left...
But we don't need to! We already know it takes 10 seconds for half of the substance to decay. So if we start with 16 grams, then after 10 seconds, 8 grams will remain.
10s later (after a total of 20 seconds), 4g will remain.
10s later (30s), 2g will remain.
10s later (40s), 1g will remain.
10s later (50s), 1/2 g will remain.
So first 15/100 which is 15 percent and out of 20, thats 15.
20. 100. 100X15 divided by 20 which is 75. I did cross multiplication ok. So I just did 20 times 15 and then divided by 100
You would cross multiply.
14 over 31.5
and X over 10.5
10.5 times 14 is 147
divide that by 31.5 which is 4 1/3
and that is how fast she can run
4 1/3 mph
The photo is upside down....
Increasing it by 10% will be 11.55. To find teen percent all you do is make it a decimal then multiplying it by 10.50
