The answer is b I believe
Answer:
64. 6138
66. 8.078125
Step-by-step explanation:
Let's take it one number at a time.
For number 64:










Sum = 6 + 12 + 24 + 48 + 96 + 192 + 384 + 768 + 1536 + 3072
Sum = 6138
For number 66:










Sum = 12 + -6 + 3 + -1.5 + 0.75 + -0.375 + 0.1875 + -0.0078125 + 0.046875 + -0.0234375
or to make things simpler:
Sum = 12 - 6 + 3 - 1.5 + 0.75 - 0.375 + 0.1875 - 0.0078125 + 0.046875 - 0.0234375
Sum = 8.078125
Answer:

Step-by-step explanation:
We can directly substitute y of the first equation to the second equation.
-2x - 1 = 3x - 16
5x = 15
x = 3
Substituting back to any of the two equations, we get y = -2(3)-1 = -7. If you check with the second equation, y = 3(3)-16 = -7 as well.
Therefore
.
Option B:

Solution:
Given sound level = 120 decibel
To find the intensity of a fire alarm:

where 
Step 1: First divide the decibel level by 10.
120 ÷ 10 = 12
Step 2: Use that value in the exponent of the ratio with base 10.

Step 3: Use that power of twelve to find the intensity in Watts per square meter.


Now, do the cross multiplication,




Option B is the correct answer.
Hence
.
Answer: a - 4.512 hours
b - 1.94 hours
Step-by-step explanation:
Given,
a) A(t) = 10 (0.7)^t
To determine when 2mg is left in the body
We would have,
A(t) = 2, therefore
2 = 10(0.7)^t
0.7^t =2÷10
0.7^t = 0.2
Take the log of both sides,
Log (0.7)^t = log 0.2
t log 0.7 = log 0.2
t = log 0.2/ 0.7
t = 4.512 hours
Thus it will take 4.512 hours for 2mg to be left in the body.
b) Half life
Let A(t) = 1/2 A(0)
Thus,
1/2 A(0) = A(0)0.7^t
Divide both sides by A(0)
1/2 = 0.7^t
0.7^t = 0.5
Take log of both sides
Log 0.7^t = log 0.5
t log 0.7 = log 0.5
t = log 0.5/log 0.7
t = 1.94 hours
Therefore, the half life of the drug is 1.94 hours