The mean age of a group of students is 16. John joins the group and the mean age changes to 18. How old is john ?
1 answer:
Answer:
John is 20 years old.
Step-by-step explanation:
Given the second mean is 18, it is equal to the first mean age plus John's unknown age. The sum is also divided by 2 because there are 2 values in the sum (1. John's age and 2. the mean, 16 yrs old).
Set up an equation:
multiply both sides by 2:
simplify:
You might be interested in
I believe you are referring to the half-life formula, which is used to calculate the half-life (when the substance drops to half of its original amount) of radioactive substances. The equation is as follows: 
<em>A</em> is the remaining amount
<em>P</em> is the initial amount
<em>t</em> is the time that has passed
<em>h</em> is the half-life of the substance
When plugging values into the equation, make sure that <em>t </em>and <em>h </em>are both measured in the same unit (e.g. <em>t </em>days and <em>h </em>days), as well as <em>A </em>and <em>P</em>.
<em>A</em> is the remaining amount
<em>P</em> is the initial amount
<em>t</em> is the time that has passed
<em>h</em> is the half-life of the substance
When plugging values into the equation, make sure that <em>t </em>and <em>h </em>are both measured in the same unit (e.g. <em>t </em>days and <em>h </em>days), as well as <em>A </em>and <em>P</em>.
Let W = number of white cars, and Y = number of yellow cars.
There were 9 times as many white cars as yellow cars. This means that the number of white cars was 9 times more than the number of yellow cars. This can be translated by the expression:
9Y = W
The person counted 40 cars in total:
W + Y = 40
So we get the system:
In the first equation, we multiply by 9:
9W + 9Y = 360
In the second equation:
9Y= W
W-9Y = 0
Then we add the first with the second equation:
9W + 9Y + W - 9Y = 360
10 W = 360
W = 36
So He counted 36 white cars.
Hope this Helps! :)
There were 9 times as many white cars as yellow cars. This means that the number of white cars was 9 times more than the number of yellow cars. This can be translated by the expression:
9Y = W
The person counted 40 cars in total:
W + Y = 40
So we get the system:
In the first equation, we multiply by 9:
9W + 9Y = 360
In the second equation:
9Y= W
W-9Y = 0
Then we add the first with the second equation:
9W + 9Y + W - 9Y = 360
10 W = 360
W = 36
So He counted 36 white cars.
Hope this Helps! :)
Since the sum of the probabilities of all possible outcomes must be 100%, we can deduce the following:
- Cooking in under 20 minutes: 10%
- Cooking between 20 and 30 minutes: 85%
- Cooking in more than 30 minutes: 5%
In fact, the probabilities of cooking in less than 20 or more than 30 sum up to 15%, which means that the remaining outcome (i.e. cooking time between 20 and 30) must complete this probability to 15, and in fact 15+85=100.
That being said, all three answers are simply a combination of these three scenarios: let C be the cooking time, for aesthetic reasons: