Answer:
$17
Step-by-step explanation:
Books = x
1. Set up an equation.
147 - 8x = 11
2. Solve for x
147 - 8x = 11
-8x = 11 - 147
-8x = -136
x = -136 / (-8)
x = 17
So, each book cost $17.
-#(1(1+#&$:3:+343;2()1-^|•{`}÷~^¢™¢
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.
