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Elina [12.6K]
3 years ago
10

How long will it take for 2 g of a sample of iodine-131, which has a half-life of about 8 days, to decay to 0.04 g?

Mathematics
1 answer:
Zigmanuir [339]3 years ago
6 0
We know that

<span>This problem can be represented through the following equation
</span>
A = A₀(1/2)^t/h
where
A----------->  is the amount of substance left after time t
A₀ ----------> is the original amount---------> 2 g
h------------->  is the half-life-----------> 8 days

for A=0.04 g
t=?
0.04 = 2(1/2)^t/8
0.02 = (1/2)^t/8
Take ln on both sides:
ln(0.02) = ln [(1/2)^t/8]
ln(0.02) = (t/8)(ln 1/2)
t = 8*ln(0.02)/ln(1/2)
t = 45.15 days

the answer is 45.15 days
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The sum of interior angles in a triangle are 180 degrees. Angle B and C are congruent. Angle B is twenty less than angle A. Writ
Margarita [4]

Answer:

A = 73.33

B = 53.33

C = 53.33

Step-by-step explanation:

Mathematically, adding the 3 angles would equal 180

Thus;

A + B + C = 180 •••••(i)

Since B and C are congruent, that means they are equal ( we are looking at isosceles triangle)

B = C •••••••••(ii)

Lastly;

B = A -20 ••••••••(iii)

Make a substitution in equation 1;

A + A -20 + A -20 = 180

Since B = C ; C also is A-20

3A -40 = 180

3A = 220

A = 220/3 = 73.33

B = C = A -20 = 73.33 -20 = 53.33

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3 years ago
Listen
makkiz [27]

Answer:

The answer is the third equation. A = 250*(1 +0.016)^(0.75)

Step-by-step explanation:

Since Javier deposited $250 into an account with annual interest rate, then as the years passes his account will grow in the manner shown below:

account(0) = 250

account(1) = account(0)*(1 + 1.6/100) = account(0)*(1 + 0.016) = account(0)*1.016

account(2) = account(1)*1.016 = account(0)*1.016*1.016 = account(0)*(1.016)²

account(3) = account(2)*1.016 = account(0)*(1.016)²*1.016 = account(0)*(1.016)³

account(n) = account(0)*(1.016)^n

Where n is the number of years, account(0) is the initial amount. In this case only 9 months have passed, so we need to convert this value to years, dividing it by 12, which is 9/12 = 0.75. The initial amount was 250, so the equation is:

A = 250*(1.016)^(0.75)

The answer is the third equation.

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Answer:

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Step-by-step explanation:

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