Overall, the goal is to find the value of x and then use this and the given total to find the percentage of x. First, to do this, we must set up our equations based on the given information.

x + y + z = 510

z = (3/2)y

y = 3x

Now, we can begin to solve with substitution. The ultimate goal is to get the first equation to be regarding one variable and them work backwards using that found value.
Substitute the 3rd equation into the second.

z = (3/2)(3x) ----> Simply
z = (9/2)x

Now, when we plug in z and y into the first equation, only x will be present.

x + (3x) + (9/2)x = 510 ---> Combine like terms.
4x + (9/2)x = 510 ---> Get a common denominator.

(8/2)x + (9/2)x = 510

(17/2)x = 510 -----> Multiply both sides by 2/17

Now, if you understand what you are looking at, you know that you just found your answer which is 2/17 because you are about to multiply that by the total.

2/17 = .12 × 100 = 12%

If you did not know that, you can continue solving and then find the answer using part over whole or the total books of school x divided by the total books from all schools. You will get the same answer!

x = (2/17)×510
x = 60

60/510 = .12 × 100 = 12%

I hope this helps!

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4 years ago