Question

http://emathinstruction.com/wordpress/wp-content/uploads/2014/11/CCAlg1-U6L7-Exponential-Models-Based-on-Percent-Growth.pdf

Can someone help me please ? My questions that i need help with are on page 4. Just click the link and scroll down to the last page which is page 4.

Answer 1

Q4?

Answer 2

what is q4 @phi

Answer 3

which question 4 or 5 ?

Answer 4

both @phi

Answer 5

4 a) what % is the material decaying per day.
First, if you start with 100 and go to 90 you have 90/100 = 90% left and you "lost" 10%
it decays by 10%

if you start with 100 and go to 80, you have 80% left and you lost 20%

In your problem you multiply by 0.88 (each day). in other words, you will have 88% left over. How much did you lose ?

Answer 6

a(d)=450(0.88)^88

Answer 7

like this @phi

Answer 8

no. Here is another way to do it.
how much stuff do you have on day 0 ?

Answer 9

to find out , use d=0 in your formula

Answer 10

hold on

Answer 11

i get 450 when d=0

Answer 12

yes,
\[ 450 \cdot 0.88^0 = 450 \cdot 1 = 450\]
anything to the "zero power" is 1

now how much stuff do you have on day 1 (d=1) ?

Answer 13

i get 3.96 when d=1

Answer 14

you mean 396

now how much stuff have we lost going from 450 to 396 ?

Answer 15

\[ 450 \cdot 0.88^1 = 450\cdot 0.88= 396\]

Answer 16

ok

Answer 17

which one is the answer for 4a ?

Answer 18

how much stuff have we lost going from 450 to 396 ?

Answer 19

54 @phi

Answer 20

yes, we lost 54
the fraction lost is "amount lost" divided by "original amount"
so we want to change
\[ \frac{54}{450} \] into a decimal
then multiply by 100 to make it a % lost (which will be the answer to 4a)

Answer 21

12 % @phi

Answer 22

yes.

The other way to do the problem is to know that when we multiply by 0.88
we have 88% left and we lost 100%-88%= 12%

Answer 23

b) A(14)= 75
what does this mean?
what does A stand for (read the first part of the question) ?

Answer 24

A stand for( in grams of a radioactive material that is decaying) @phi

Answer 25

ok, and what does the 14 stand for in A(14) (based on the formula)

Answer 26

a(14) stands for the days since it started decaying @phi

Answer 27

ok, so A(14) means (in short-hand)
grams of radioactive material left after 14 days

A(14) = 75
the equal sign means "is"

translated, this means
grams of radioactive material left after 14 days is 75

Answer 28

or, to write it in better English

A(14)=75 means

75 grams of radioactive material is left after 14 days.

Answer 29

For 4c)
mark 5 "hash marks" on the y-axis
and label them 100 , 200, etc up to 500