I need help with my Algebra II please. *STORY PROBLEMS* heck yeah! Sorry, lol. Well, 8 of the 10 are story problems.

FIND THE NUMBER DESCRIBED #2-4:
2. 12 is 3/5 of 10/21 of the number. DONE WITH!

4. 75% of 60% of the number is 36. DONE WITH!

6. An old conveyor belt takes 21 h to move one day's coal output from the mine to a rail line. A new belt can do it in 15 h. How long does it take when both are used at the same time?

8. How much water must be evaporated from a 300 L tank of a 2% solution to obtain a 5% solution?

10. Pam jogged up a hill at 6 km/h and then jogged back down at 10 km/h. How many kilometers did she travel in all if her total jogging time was 1 h 20 min.?

12. Lina Chen invested $24,000, part at 8% and the rest at 7.2%. How much did she invest at each rate if her income from the 8% investment is two thirds that of the 7.2% investment?

14. How much of an 18% solution of sulfuric acid should be added to 360 mL of a 10% solution to obtain a 15% solution?

16. Pipes A and B can fill a storage tank in 8 h and 12 h, respectively. With the tank empty, pipe A was turned on at noon, and then pipe B was turned on at 1:30 P.M. At what time was the tank full?

18. An elevator went from the bottom to the top of a tower at an average speed of 4 m/s, remained at the top for 90 s, and then returned to the bottom at 5 m/s. If the total elapsed time was 4.5 min, how high is the tower?

20. A car radiator is filled with 5 L of a 25% antifreeze solution. How many liters must be drawn off and replaced by a 75% antifreeze solution to leave the radiator filled with a 55% antifreeze solution?

Please show the work to generate these answers and I will try to work a few of these out myself. Thank you all for your help.

(is problem #18: 810 meters high?)
(is problem #10: 10.6666666666666 km? (10.6 with a bar over the 6 kilometers)


This message was edited by wildfirefxx on Mar 30 2008.

10. 10 km. The average speed is total distance divided by total time; it can also be calculated by finding the average of all the speeds. From this,

(6 km/h + 10 km/h)/2 = D / 1.25 h
(16 km/h)/2 = D / 1.25 h
8 km/h = D / 1.25 h
1.25 h(8 km/h) = D
10 km = D

18. No. Remember that time is equal to distance divided by speed. Since the same distance is travelled during both trips, the equation would be

[4.5(60)] - 90 = d/4 + d/5,

[4.5(60)] - 90 representing the total time of both trips, in seconds (180: 4.5 minutes = 270 seconds, but we have to subtract the 90 seconds where the elevator did not move), d/4 and d/5 representing the height of the tower (d), in meters, divided by the speed of each trip (4 and 5, respectively), in meters per second. Thus, we have

180 = d/4 + d/5
180 = 5d/20 + 4d/20
180 = 9d/20
3,600 = 9d
400 = d.

Checking our answer through substitution, we get that

180 = 400/4 + 400/5
180 = 100 + 80
180 = 180.