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Algebra 2
Section 1.8
Using Formulas
Solve each problem. Use the formula i = prt.
i = interest p = principal r = rate
t = time (in years)
1. For a loan of $6,500 for 8 years, Jose was charged $3,640 in
simple interest. What was the annual interest rate?
i = prt
3,640 = 6,500(r)(8)
3640 = 52,000r
r = .07
= 7%
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2. When would a borrower owe $6,528 in simple interest on a
loan of $6,400 at 8 ½%?
= 8.5% = .085
i = prt
6,528 = 6,400(.085)(t)
6,528 = 544t
t = 12 years
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3. Ms. Brown borrowed some money on February 1, 1972, at 6% per
year. How much did she borrow if Ms. Brown paid off the debt,
including $3,000 in simple interest, on February 1, 1982?
i = prt
3,000 = p(.06)(10)
3,000 = .6p
p = $5000
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Solve the problem. Use the formula A = p + prt
4. Find p in dollars if A = $9,780, r = 9%, and t = 7 years.
A = p + prt
9,780 = p + p(.09)(7)
9,780 = p + p(.63)
9,780 = 1.63p
p = $6,000
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Solve each problem. Use the formula R(r1 + r2) = r1 · r2
5. Find R in ohms if r1 = 50 ohms and r2 = 30 ohms.
R(r1 + r2) = r1 · r2
R(50 + 30) = 50(30)
80R = 1500
R = 18.75 ohms
6. Find r2 in ohms if R = 24 ohms and r1 = 60 ohms.
R(r1 + r2) = r1 · r2
24(60 + r2) = 60r2
1,440 + 24r2 = 60r2
- 24r2
-24r2
1,440 = 36r2
r2 = 40 ohms
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For the following, use the formula h = vt – 5t2
h = height
v = initial velocity t = time (in seconds)
7. Find v in meters per second if h = 150m and t = 5 sec.
h = vt – 5t2
150 = v(5) – 5(52)
150 = 5v – 5(25)
150 = 5v – 125
+125
+125
275 = 5v
v = 55 meters per second
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8. At the end of 3 seconds, what will be the height of an arrow
if an archer shoots it upward with an initial velocity of
120 meters per second?
h = vt – 5t2
h = 120(3) – 5(32)
h = 360 – 5(9)
h = 360 – 45
h = 315 meters
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Solve each problem. Use the formula i = prt.
1.) For a loan of $2,500 for 5 yr 9 mo, Muna was charged $1,150 in simple interest.
What was the annual interest rate?
Algebra 2
Section 1.8
Assignment
2.) When would a borrower owe $1,152 in simple interest on a loan of $3,200
at 8% per year?
3.) Mr. Adamshick borrowed some money on July 1, 1974, at 7 ½ % per year. How
much did he borrow if Mr. Adamshick paid off the debt, including $1,485 in
simple interest, on October 1, 1982?
Solve each problem. Use the formula h = vt – 5t2.
4.) Find h in meters if v = 60 m/s and t = 4 s.
5.) A certain baseball pitcher can throw a ball with an initial velocity of 35 m/s.
If the pitcher throws the ball straight up, what will its height be at the end of
2 seconds and at the end of 5 seconds?
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