7_5 practice
1.
Solve the following exponential equation. Write the answer as a decimal approximation, rounded to 2
decimal places.
42x - 5 = 617
2.
Solve the following exponential equation. Write the answer as a decimal approximation, rounded to 2
decimal places.
3
6 x = 148
3.
Rhonda is saving up money for a down payment on a car. She currently has $4156, but knows she can
get a loan at a lower interest rate if she can put down $4916. If she invests the $4156 in an account
that earns 4% annually, compounded monthly, how long will it take Rhonda to accumulate the $4916?
Round your answer to 2 decimal places.
4.
Suppose a population of bacteria in a Petri dish has a tripling time of 6.5 hours. How long will it take
for an initial population of 9500 bacteria to reach 90000? Round your answer to two decimal places.
5.
Solve the following exponential equation. Write the answer as both an exact expression and as a
decimal approximation (rounded to 2 decimal places).
2e3x + 9 = 44
6.
Solve the following exponential equation. Write the answer as both an exact expression and as a
decimal approximation rounded to 2 decimal places.
3-x - 2 = 1784
1
7.
A radioactive substance decays according to A = A0e-0.0046t where A0 is the initial amount and t is
the time in years. If A0 = 220 grams, find the time for the radioactive substance to decay to 118 grams.
Round your answer to two decimal places.
8.
A radioactive substance decays according to A = A0e-0.0007t where A0 is the initial amount and t is
the time in years. If A0 = 620 grams, find the time for the radioactive substance to decay to 248 grams.
Round your answer to two decimal places.
9.
Solve the following exponential equation. Write the answer as both an exact expression and as a
decimal approximation (rounded to 2 decimal places). Use e = 2.71828182845905.
3x
2x
7
e
= 13 8
10.
In chemistry, the pH of a solution is a measure of the acidity or alkalinity of a solution. Water has a pH
of 7 and, in general, acids have a pH less than 7 and alkaline solutions have a pH greater than 7. Find
the pH of a solution with a hydronium ion concentration of 7.5 × 10-7 moles/liter. Round your answer
to 2 decimal places.
2