A pen costs twice as much as a pencil. If 7 pens and 12 pencils cost $6.50, find the cost of a pencil. I know the answer (pencil $0.25, pen $0.5), but I need to figure out how the answer is solved.

1. Observe the problem

2. Make a system of linear equations

x is pens

y is pencil

As stated in the text, x=2y

x=2y

7x+12y=6.50

Using substitution,

7(2y)+12y=6.50

14y+12y=6.50

26y=6.50

y=0.25

Substituting it back into the first equation:

x=2(0.25)

heudhduxhdnshenebdutbbt

step-by-step explanation:

hrhhdhdbbrurb ees

the answer is; biodiversity resulting from few ancestors

adaptive radiation occurs when a population is subjected to a large natural environment with spatial ecological variations. the parts of the population in the different ecologies begin to adapt to their local environments. due to non-random mating across the large populations, this causes the different populations from the large population to speciate within their local environments. they, therefore, diverge to different species sharing a common ancestor.