(2/5)+(3/(5x))=(x+5)/10
nasty fractions, we hates it forever
so
get rid of all those nasty fractions
multiply both sides by 10x
4x+6=x(x+5)
distribute
4x+6=x^2+5x
minus (4x+6) from both sides
0=x^2+x-6
factor
0=(x-2)(x+3)
set each to zero
0=x-2
2=x
0=x+3
-3=x
x=-3 and 2
3rd option is answer
Answer:
r = 7.7
Step-by-step explanation:
A = πr²
60π = πr²
r² = 60π/π
r² = 60

r = 7.746
Rounded to tenths:
7.7
Yes D is the correct option !
if you want to know how , comment, or you are good to go !
For this case we have an equation of the form:
y = A * (b) ^ t
Where,
A: initial amount
b: decrease rate
t: time in years.
Substituting values we have:
7 = A * (0.5) ^ ((1/20) * t)
For t = 45 years we have:
7 = A * (0.5) ^ ((1/20) * 45)
Clearing A:
A = 7 / ((0.5) ^ ((1/20) * 45))
A = 33.3
Answer:
the density of the substance when it was deposited 45 years ago was:
A = 33.3 milligrams per square centimeter