(6•8)+(4•10)+(4•6)+(4•8) = 144
Answer:
(a) A = (20mg)/(2^(t/30))
(b) 12.6mg
(c) 129.6years
Step-by-step explanation:
To calculate the amount remaining after a number of half-lives, n, we can make use of:

Where A = amount remaining
B = initial amount

(a) A = (20mg)/(2^(t/30))
(b) Mass after 20years
A = (20mg)/(2^(20/30)) ≈ 12.6mg
(c) After how long will only 1mg remain:
1mg = (20mg)/(2^(t/30))

Taking log of both sides we have:
Log(20) = (t/30)log(2)
t/30 = (log(20))/(log(2)) ≈ 4.3
t/30 = 4.3
t = 30 x 4.3 ≈ 129.6years.
X+4=-14
x=-14-4
x=-18
so basically it’s -18
Answer: C = 150$
Explanation:
C = chair
T = table
C = 10% of T
C = 10/100 x T
C = 1/10 x T
And
T + 4C = 2100$
T + 4(1/10 x T) = 2100$
T + (4T/10) = 2100$
T + 2T/5 = 2100$
5T + 2T = 10500$
7T = 10500$
T = 1500$
But C = (1/10)T
=> C = 1/10 x 1500$
C = 150$
So they pay $1,260 in interest with I=PRT
add that to the principle, which gives you $3,660