Answer:
give me a minute to find the answer
Answer:
as written: 2500.2
as intended: 3000
Step-by-step explanation:
20% = 0.2, so adding 0.2 to 2500 gives 2500.2
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We suspect you want to add 20% of 2500 to 2500. That is ...
2500 + 20%×2500
= 2500 + 0.20×2500
= 2500 + 500
= 3000
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<em>Comment on percentages</em>
A percentage is a pure number. It is a ratio of like quantities, so has no units.* A <em>useful</em> percentage always has a base. That is, it is a percentage <em>of something</em>. Sometimes that base may be unclear or unstated, in which case the percentage might very well be considered to be meaningless.
In any event, a percentage is simply a (unitless) fraction. The "%" symbol means the same thing as "/100", so 20% means 20/100 = 2/10 = 1/5.
The very clear math expression 2500 +20% means simply 2500 + 1/5, which is the mixed number 2500 1/5 or the decimal value 2500.2. Usually, when we want to add a percentage to some value, we want the percentage to be <em>of the original value</em>. When that is written as a math expression, it must show this:
2500 + 20% of 2500
2500 + 20%×2500
2500(1 +20%)
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* The concentration or potency of some medicines or other mixtures may be expressed as a percentage that is the ratio of one unit to a different unit, typically weight per volume. That is, a "0.1%" preparation may be 0.1 grams per 100 mL, for example. You have to read the label to determine whether this is the case. Mathematically, this is not a percentage, but is a non-standard use of the "%" symbol to indicate a ratio to 100 of something.
You are to find the rate of change of B with respect to t, dB/dt. Differentiate the first equation with respect to t.
dB/dt = 0.007(2/3)(W^-1/3)(dW/dt)
We have to determine W and dW/dt.
For W when L = 18 cm, we use the second equation
W = 0.12(18^2.53) = 1,800 g
For dW/dt, differentiate the second equation with respect to t.
dW/dt = 0.12(2.53)(L^1.53)(dL/dt)
We still have to find dL/dt from the given information. The solution would be:
dL/dt = (20 cm - 15 cm)/10,000,000 years = 5×10⁻⁷ cm/y
So,
dW/dt = 0.12(2.53)(18^1.53)(5×10⁻⁷) = 1.26×10⁻⁵ g/y
Now that we know W and dW/dt, we can finally solve for dB/dt.
dB/dt = 0.007(2/3)(W^-1/3)(dW/dt)
dB/dt = 0.007(2/3)(1800^-1/3)(1.26×10⁻⁵) =
<em>1.04×10⁻⁸ g/y</em>