(8x2.3)= (18.4)
(2.1x4)= (8.4)
Now you should have:
41-9+18.4-15+8.4
9+18= 27
15+8.4= 23.4
Should have:
41-27-23.4= -9.4
Answer:
The numbers are 23 and 7
Step-by-step explanation:
1. Set up the equations
Let x = the greater number
and y = the smaller number. Then
(1) x - y = 16
4y = 4 times the smaller number and
4y - 5 = 5 less than 4 times the smaller number. Then
(2) x = 4y - 5
You have a system of two equations:

2. Solve the equations

The larger number is 23; the smaller number is 7.
3. Check

OK.
Physical, you aren't changing the substance, you are just changing the shape of the cookie
The half-life of Po is 139 days, so its decay rate is
0.5 = e^(139k) ==> k = ln(0.5)/139
After some time t, 80% of the material will have decayed and you'll be left with a sample 20% of its original mass:
0.2 = e^(kt) ==> t = ln(0.2)/k = ln(0.2)/ln(0.5) * 139 = 322.748
so your sample is usable for about 323 days.