# Ratio and proportion

1. Oct 12, 2009

### xbebegirlx

If 100 bu of corn per acre remove 90lb of nitrogen, phosphorus, and potassium (N, P, and K, respectively), how many pounds of N, P, and K are removed by the yield of 135u per acre?

I try to figure out how to starting to solve this problem but dont know how

2. Oct 12, 2009

### Staff: Mentor

This is hardly a "Calculus and Beyond" problem. A better place would be the Precalculus section.

Wouldn't the ratio of 100 bu of corn to 90 lb N, P, and K be the same as the ratio of 135 lb corn to X lb of N, P, and K?

3. Oct 12, 2009

### xbebegirlx

I am still confuse dont know how to start, the bu and lb are same thing?

4. Oct 12, 2009

### Staff: Mentor

No, they're not. bu stands for bushel, a unit of volume, and lb stands for "pound", a unit of weight.

Start by translating this sentence into an equation: Wouldn't the ratio of 100 bu of corn to 90 lb of fertilizer be the same as the ratio of 135 lb corn to X lb of fertilizer?

5. Oct 13, 2009

### xbebegirlx

ok here I got 100bu/90lb=135bu/xlb
then I cross multiply
90*135 = 12150/100
= 121.5lb
please advise me see if this is right

thanks

6. Oct 14, 2009

### Staff: Mentor

Yes.
Where did x go? You started with an equation with x, and you should end up with an equation that has x = ...