Question

Could anyone help me with this problem? I understand that you can cross multiply but is there a shorter way?

Three pounds of lawn seed cover 1800 square feet. How many bags are needed to cover 8400 square feet?

Please explain and not just give the answer. I need to know how to do this in a quicker manner if possible.

Answer 1

There are several steps needed. I'm not sure this is what you call a shorter way, but I hope it helps!! :)

1) 3 lbs covers 1800 ft2 but we need to find how many ft2 1lb will cover. Divide # of lbs of seed available (3 lbs in this case) into the # of ft2 the available seed will cover (1800ft2 in this case):
1800ft2/3lbs=600ft2

So 1 lb covers 600ft2.

2) Now to find how many lbs 8400 needs. Divide the # of ft2 for 1 lb into the # of ft2 total (8400ft2 in this case):
8400/600ft2 (for 1lb) = 14 lbs

3) 14 lbs is now how many bags? The question does not say how many lbs in 1 bag.

IF ASSUMING the bags are 3lbs each, you divide the # of lbs per bag into the # of total lbs (14lbs in this case).

14lbs/3lb bags= 4.7 bags needed

IF 4lb bags:
14lbs/3lb bags= 3.5 bags needed

IF 5lb bags:
14lbs/5lb bags= 2.8 bags needed

IF 6lb bags:
14lbs/6lbs= 2.3 bags needed