Let's call the first unknown integer x and the second one y.
"Four times an unknown integer"
"Multiplied by three times the unknown integer plus a different unknown integer"
- 4x is multiplied by 3x+y, so 4x(3x+y)=12x²+4xy
"Equals 100."
And so the answer is C: 12x²+4xy-100=0
X-13=42
x is the "variable", you're taking 13 away from that, and the answer is also given, 42.
42,600 - 25,800 = 16800. That is the increase in 15 years.
You then calculate the increase as a percentage of the original population; 25,800.
16,800 / 25,800 * 100 = 65.11%
3 x
---------= --------- ---------
15 180
15x=540
----- ------= 36 students.
15 15
Steps: Cross multiply to get 15x and 540. Divide both numbers by 15, then you found what x equals, which is the answer.
