With the information given we can wirte down 2 different equations where:
x = How many Fictoon books there are
A nd y = How many non-fiction books there are :
#1) x + y = 312
( The total of the books is 312 )

#2) x = 11y
(He has 11 times as many firction books as he has non-ficton books)

Now what we need to do is to isolate one the variables ( x or y ) , get its value and apply to one the equations to get the other variable's value:
We can do that by the property of substitution:

If x = 11y
then x + y = (11y) + y = 12y

If x + y = 312
and x + y = 12y
then 12y = 312

Now with the equation 12y = 312 , we can isolate y by dividing both sides of the equation by 12 :
12/12y = 312/12
y = 26
What that means : Mark has 26 non-fictional books.

Now that we have the value of y , we can find the value of x by plugging y to one of the equations :

x + y = 312
or
x = 7y
( I will do both , but you dont need to )

x + y = 312
Plugin 26 for y :
x + 26 = 312

Shift 26 to the other side of the equation by subtracting both sides of the equation by 26:
x + 26 - 26 = 312 - 26
26 - 26 cancel out , so we end up with :
x = 286

Second Equation :
x = 11y
Plugin 26 for y:
x = 11 × 26

x = 286

Awnser : Mark has 286 fictoon books and 26 non-fiction !

I hope you understood my brief explanation. And please consider marking this awnser as Branliest. Thank you ! :)

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4 years ago