18. a square has an area of 81 square inches....
18. a square has an area of 81 square inches. the length of each side is ____ inches. a. 7.9 b. 9 c. 11 d. 17\n19. a bottle contains 11 pints of liquid. to this bottle 1.32 pints is then added. this is an increase of a. 6% b. 9% c. 12% d. 16%\n20. a week ago a storage battery read 12.4v. today its voltage is 8.1% less. its voltage is now a. 11.4 b. 10.8 c. 9.3 d. 10.2\n21. the advantage of a vacuum tube voltmeter over a regular voltmeter is that it a. operates on batteries b. operates on 120v ac c. has a low input impedance d. has a high input impedance
Answer
# Explanation:
## Step1: Calculate triangle area
For a right - angled triangle with sides 3 inches and 4 inches, use the area formula $A=\frac{1}{2}\times base\times height$. Here, $A = \frac{1}{2}\times3\times4=6$ square inches.
## Step2: Find side length of square
Given the area of a square $A = s^{2}$ (where $s$ is the side - length) and $A = 81$ square inches. Then $s=\sqrt{81}=9$ inches.
## Step3: Calculate percentage increase of liquid
The original amount of liquid is 11 pints and 1.32 pints are added. The percentage increase formula is $\text{Percentage increase}=\frac{\text{Increase}}{\text{Original amount}}\times100\%$. So, $\frac{1.32}{11}\times100\% = 12\%$.
## Step4: Calculate new voltage of battery
The original voltage of the battery is $V_0 = 12.4$V and it is 8.1% less. The new voltage $V=V_0(1 - 0.081)=12.4\times(1 - 0.081)=12.4\times0.919 = 11.4$V.
## Step5: Recall vacuum tube voltmeter property
A vacuum - tube voltmeter has a high input impedance compared to a regular voltmeter.
# Answer:
17. A. 6
18. B. 9
19. C. 12%
20. A. 11.4
21. D. has a high input impedance