Rory records the percentage of battery life remaining on his phone throughout a day. The battery life decreases as Rory uses the phone, but will increase or stay at 100% while charging. The graph represents the percentage of battery life remaining after a certain number of hours. A graph titled Phone Battery Life. The horizontal axis shows Elapsed Time (hours) numbered 2 to 20, and the horizontal axis shows Battery Life (%) numbered 10 to 120. A line begins at 100% in 0 hours, to 20% in 8 hours, to 100% from 10 to 12 hours, to 60% in 16 hours, to 100% from 17 to 20 hours.

At which times could Rory's phone have been plugged into the charger? Select three options.

9 hours

11 hours

19 hours

Step-by-step explanation:

The graph represents the percentage of battery life remaining after a certain number of hours is attached below.

At which times could Rory's phone have been plugged into the charger? Select three options.

6 hours

9 hours

11 hours

14 hours

19 hours

From the graph, the line segment with negative slope (that is decreasing value) shows that the phone is not plugged but being used while the line segment with positive slope (increasing value) or stays at 100% shows that the phone is plugged to the charger.

As shown, from 0 to 8 hours their is a decreasing value, the phone is not plugged. From 8 to 10 hours their is an increasing value therefore the phone is plugged also from 10 to 12 hours the phone is plugged since it is constant. From 12 to 16 hours it is not plugged. From 16 to 18 hours it is plugged and from 18 to 20 hours it is plugged.

From the options it is plugged at 9 hours, 11 hours and 19 hours

if x decreases by 4 then y increases by 10

step-by-step explanation:

i think it's eleven too, don't woosh me here, but according to the "experts" it's 2.

the proof starts from the peano postulates, which define the natural

numbers n. n is the smallest set satisfying these postulates:

  p1.   1 is in n.

  p2.   if x is in n, then its "successor" x' is in n.

  p3.   there is no x such that x' = 1.

  p4.   if x isn't 1, then there is a y in n such that y' = x.

  p5.   if s is a subset of n, 1 is in s, and the implication

      (x in s => x' in s) holds, then s = n.

then you have to define addition recursively:

  def: let a and b be in n. if b = 1, then define a + b = a'

      (using p1 and p2). if b isn't 1, then let c' = b, with c in n

      (using p4), and define a + b = (a + c)'.

then you have to define 2:

  def:   2 = 1'

2 is in n by p1, p2, and the definition of 2.

theorem:   1 + 1 = 2

proof: use the first part of the definition of + with a = b = 1.

      then 1 + 1 = 1' = 2   q.e.d.

note: there is an alternate formulation of the peano postulates which

replaces 1 with 0 in p1, p3, p4, and p5. then you have to change the

definition of addition to this:

  def: let a and b be in n. if b = 0, then define a + b = a.

      if b isn't 0, then let c' = b, with c in n, and define

      a + b = (a + c)'.

you also have to define 1 = 0', and 2 = 1'. then the proof of the

theorem above is a little different:

proof: use the second part of the definition of + first:

      1 + 1 = (1 + 0)'

      now use the first part of the definition of + on the sum in

      parentheses:   1 + 1 = (1)' = 1' = 2   q.e.d.