Alex determined that his average speed when he commuted to work is 35 miles per hour. What conversion factor can be used to conv
2 answers:
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Answer:
After 9 more minutes, her cell battery will be 80% charged.
Explanation:
Let us try to make an equation here to describe the relation between battery and time.
It is given that the battery charges at a constant rate so we can assume that
battery() ∝ Time(
)
But at t=0, the battery is already 30% charged so we rewrite the equation as follows:
-(1)
Now,
at put t=36 and b=70 in Eqn 1:
We get
The final eqn is
Put b=80
We get:
∴ It will take (45-36)=9 more minutes to reach 80% battery.
#SPJ2
<h3>Answer:</h3>
60 days
<h3>Explanation:</h3>Half-life is the amount of time it takes half of a substance to decay away.
Guess and Check
One method for solving half-life problems like this is to guess and check. To do this, we can continue to divide 475mg by 2 until we get to 30mg.
- 475 ÷ 2 = 237.5
- 237.5 ÷ 2 = 118.75
- 118.75 ÷ 2 = 59.375
- 59.375 ÷ 2 = 29.6875
As seen here, it takes approximately 4 half-lives for this sample of Ra-225 to decay to 30mg. Now, we can multiply 4 by the length of the half-life, 15 days.
- 4 * 15 = 60 days.
Fractions
Another way to solve this is to use fractions.
- 30 is about 1/16 of 475
- 16 is equivalent to
.
This means that it takes 4 half-lives for 475mg to decay to 30mg. Using the same method above, we can tell that 4 half-lives are 60 days.
Important Note
In this question, I rounded occasionally. So, not all of the values are exact, but they are all very close.