Penelope invested $6650 into theee investment accounts, earning 8%, 12.5%, and 7.5% simple interest per year. If the annual interest earned totaled $671.25 and the amount invested at 12.5% was $300 more than twice the amount invested at 8%, find the amount invested into each account.

$1500 was invested in the account earning 8%.

$3300 was invested in the account earning 12.5%.

$1850 was was invested in the account earning 7.5%.

Step-by-step explanation:

Let x represent the amount invested in the account earning 8%.

Let y represent the amount invested in the account earning 12.5%.

Let z represent the amount invested in the account earning 7.5%.

Penelope invested $6650 into theee investment accounts, earning 8%, 12.5%, and 7.5% simple interest per year. It means that

x + y + z = 6650- - - - - - - - - - -1

Interest earned from the $x investment is

8/100 × x = 0.08x

Interest earned from the $y investment is

12.5/100 × x = 0.125y

Interest earned from the $z investment is

7.5/100 × x = 0.075z

If the annual interest earned totaled $671.25, it means that

0.08x + 0.125y + 0.075z = 671.25- - - - - - - 2

The amount invested at 12.5% was $300 more than twice the amount invested at 8%. It means that

y = 2x + 300

Substituting y = 2x + 300 into equation 1 and equation 2, it becomes

x + 2x + 300 + z = 6650

3x + z = 6650 - 300

3x + z = 6350- - - - - - - - - 4

0.08x + 0.125(2x + 300) + 0.075z = 671.25

0.08x + 0.25x + 37.5 + 0.075z = 671.25

0.33x + 0.075z = 671.25 - 37.5

0.33x + 0.075z = 633.75- - - - - - - 5

From equation 4, z = 6350 - 3x

Substituting z = 6350 - 3x into equation 5, it becomes

0.33x + 0.075(6350 - 3x) = 633.75

0.33x + 476.25 - 0.225x = 633.75

0.33x - 0.225x = 633.75 - 476.25

0.105x = 157.5

x = 157.5/0.105

x = 1500

y = 2x + 300

y = 2(1500) + 300

y = 3300

Substituting x = 1500 and y = 3300 into equation 1, it becomes

1500 + 3300 + z = 6650

z = 6650 - 4800

z = 1850

step-by-step explanation: so we look at the formula un = a + (n-1)d

un is the amount of seats

n is the nth term aka row number

a is the original sequence/row number

d is the difference between each term

so in this a=22 d=6 and n can remain as n because we are simply formjng a rule

lets put these in the equation

un=22+(n-1)(6)

this is your answer to part a

however

lets double check that this is correct, we'll try putting it into the second term

un=a+(n-1)d

u2=22+(2-1)(6)

u2=22+6

u2=28

as the question said the second row has 28 seats so now we know the formula we made is correct.

as for part b

un=a+(n-1)

its asking us to find a row with 100 seats.

remember un was the amount of seata so all we do is substitute this in.

un=100 a=22 d=6

un=a+(n-1)d

100=22+(n-1)(6)

so now we simplify to find n which is the row number.

100-22=22+(n-1)(6)-22

78=(n-1)(6)

78/6=(n-1)(6)/6

13=n-1

13+1=n-1+1

14=n

so now we know that in the 14th row there is 100 seats.

hope this and that you understood! its my first time using the app or anyone out on here : p its also me to revise so a bunch! ask more questions if you dont understand ☺