Mat 126
posted by Derek .
A community college has 3,000 students and 90 instructors. The college plans that enrollment will be 3,500 next year. How many new instructors should be hired if the college wants to keep the same student to instructor ratio?
13 instructors
15 instructors
105 instructors
77 instructors

Ratio:
3000/90 = 3500/x
Cross multiply:
3000x = 315000
x = ? 
Cross multiply 3000/90=3500/x
3000x=315,00 divide each side by 3000 and you get x=105 then take 105 and subtract from the original number of 90 and you get 15. So they need to hire 15 more instructors to keep the same student/teacher ratio. 
A person hires his firm to build a Cb radio tower. The firm charges $100 for labor for the first ten feet.
After, that the cost of the labor for each succeeding 10 feet is $25 more than the preceding 10 feet. That is, the next feet will cost $125, the next 10 feet will cost $150, etc. How much will it cost to build a 90foot tower?