Question

After how many days do only 4/5 of the students recall the important features of the classroom lecture? There are two parts to this questionIt says locate the point on the graph that conveys this information

Answer 1

Given:

`P(x)=90-25log_2x`

Required:

We need to find the value of x when P(x)=80.

Step-by-step explanation:

`Substitute\text{ P\lparen x\rparen=80 in the equation }P(x)=90-25log_2x.`

`80=90-25log_2x`

Solve for x.

`25log_2x=90-80`

`25log_2x=10`

Divide both sides by 25.

`(25log_2x)/(25)=(10)/(25)`

`log_2x=(2)/(5)`
`Use\text{ If }log_bx=y\text{ then }b^y=x.\text{ here b=2 and }y=(2)/(5).`
`x=2^{(2)/(5)}`
`x=2^(0.4)`
`x=1.3\text{ days.}`

Final answer:

`x=1.3\text{ days.}`

See a horizontal line from point 80 on the y axis and mark the intersection point on the graph.