12 x 80 = 960
18 x 86 = 1548
960 + 1548 = 2508
12 + 18 = 30
2508/30 = 83.6
The class average is 83.6
There are 77,600,000 pet cats rounded to the nearest hundred thousand because of the rule that if its over 5 round up under round down and 5>2 so the answer is 77,600,000
475 songs- 380 songs= 95 songs
95 songs/ 475 songs* 100%= 20%
The percent error is 20%~
Start by writing out the information you know mathematically (I used S for cost of senior ticket, and C for cost of child ticket. You could use X and Y, or any other combination of letters as variables)
3s + 1c=38
3s + 2c=52
Now, you'll want to eliminate one of the variables by subtracting it out. Remember - Same sign, subtract (and therefore different sign, add).
In this case, 3s exists in the first and second equation, so it's very easy to get rid of. They're both positive, so they have the same sign (+). Same sign, subtract.
3s + 1c=38
-(3s + 2c=52)
__________
0 -1c= -14
-c=-14
C=14
Now, plug c=14 into either of the original equations.
3s + C= 38
3s + 14=38
3s=24
S=8.
So, a child ticket costs $14 and a senior ticket costs $8.