You put $1000 into an investment yielding 6% annual interest; you left the
money in for two years. How much interest do you get at the end of those two
years?
In this case,
P
= $1000,
r
= 0.06 (because I have to convert the percent to
decimal form), and the time is
t
= 2. Substituting, I get:
I = (1000)(0.06)(2) = 120
I will get $120 in interest.
examples

You put
$1000
into an investment yielding
6%
annual interest; you left the money in for two years.
How much interest do you get at the end of those two years?
In this case,
P
= $1000,
r
= 0.06
(because I have to convert the percent to decimal form), and
the time is
t
= 2
. Substituting, I get:
I = (1000)(0.06)(2) = 120
I will get
$120
in interest
You invested
$500
and received
$650
after three years. What had been the interest rate?
For this exercise, I first need to find the amount of the interest. Since interest is added to the
principal, and since
P
= $500,
then
I
= $650 – 500 = $150
. The time is
t
= 3
. Substituting
all of these values into the simple-interest formula, I get:
150 = (500)(
r
)(3)
150 = 1500
r
150
/
1500
=
r
= 0.10
4.Mixture problems
Mixture problems involve creating a mixture from two or more things, and then
determining some quantity (percentage, price, etc) of the resulting mixture.
Example:
Your school is holding a "family friendly" event this weekend.
Students have been pre-selling tickets to the event; adult tickets are $5.00, and
child tickets (for kids six years old and under) are$2.50. From past experience, you
expect about13,000 people to attend the event. But this is the first year in which
tickets prices have been reduced for the younger children, so you really don't know
how many child tickets and how many adult tickets you can expect to sell. Your boss
wants you to estimate the expected ticket revenue. You decide to use the
information from the pre-sold tickets to estimate the ratio of adults to children, and
figure the expected revenue from this information.
You consult with your student ticket-sellers, and discover that they have not been
keeping track of how many child tickets they have sold. The tickets are identical,
until the ticket-seller punches a hole in the ticket, indicating that it is a child ticket.

But they don't remember how many holes they've punched. They only know that
they've sold 548tickets for $2460. How much revenue from each of child and adult
tickets can you expect?

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- Fall '19
- Numerical digit, Decimal, Miguel