# A life of a bulb is partly constant and partly inverse proportional to its average usage. When average usage is 10 hours its life is 810 hours, when average usage is 20 hours its life is 805 hours. If the life of bulb is 1000 hours what will be its average usage? A) 1 hour B) 2 hour C) 0.5 hour D) 1.5 hour

Asked By Achint On 08/07/2019 12:16

## Answers

Answer is C - 0.5 hours
Let the average usage be A and life of the bulb be L
We can present L as L = a + (b/A) where a and b are constants. This equation ensures that L is partially constant and partially inversely proportional to average usage A
When A is 10, L is 810 and when A is 20, L is 805. Using these values and plugging them in the equation above gives us the values of a and b
a= 800 and b =100
Now to find the value of A for L =1000, put L =1000, a=800 and b=100 in the main equation
We get A = 0.5

Answered On 08/20/2019 18:27

Answered On 08/20/2019 18:27

Login __here__ to answer this question

Click a subject below to view more math questions:

Math 6th grade 7th grade 8th grade high school pre-algebra algebra 1 algebra 2 geometry trigonometry pre-calculus calculus 1 calculus 2 college 5th grade 4th grade 3rd grade 2nd grade 1st grade

Math 6th grade 7th grade 8th grade high school pre-algebra algebra 1 algebra 2 geometry trigonometry pre-calculus calculus 1 calculus 2 college 5th grade 4th grade 3rd grade 2nd grade 1st grade