SOLUTION: An orchard has 728 pear trees. The number of rows exceeds the number of trees per row by 2. How many trees are there in each row?

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Question 1179483: An orchard has 728 pear trees. The number of rows exceeds the number of trees per row by 2. How many trees are there in each row?

Found 2 solutions by MathLover1, greenestamps:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

An orchard has 728 pear trees.
The number of rows x exceeds the number of trees y per row by 2.
x=y%2B2
x%2Ay=728...........substitute x
%28y%2B2%29y=728
y%5E2%2B2y=728
y%5E2%2B2y=728
y%5E2%2B2y-728=0
y%5E2%2B2y-728=0
y=%28-2%2B-sqrt%282%5E2-4%2A1%28-728%29%29%29%2F%282%2A1%29
y=%28-2%2B-sqrt%282916%29%29%2F2
y=%28-2%2B-54%29%2F2...take only positive solution
y=%28-2%2B54%29%2F2
y+=+26
x=26%2B2
x=28
there are 28 rows, and 26 trees per row

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Note in the solution from the other tutor how the standard algebraic solution involves factoring the quadratic equation

x%5E2%2B2x-728=0

Few people are going to look at that and see that the factorization is

%28x%2B28%29%28x-26%29=0

In their solution, they solved the equation using the quadratic formula. That always works; but in this case it still involved working with large numbers.

This is an example of a problem where a bit of insight (or perhaps a lot of experience) can make solving the problem much easier.

Here is what I saw almost immediately on reading the problem: we have two numbers that differ by 2 whose product is 728. That is two numbers that are very close together, so the 728 is very close to a perfect square. So instead of calling the numbers x and x+2....

let x-1 be the smaller number (number of trees per row)
let x+1 be the larger number (number of rows of trees)

Then the given information yields an equation that is solved relatively easily:

%28x-1%29%28x%2B1%29=728
x%5E2-1=728
x%5E2=729
x=27

ANSWER: The number of trees in each row is x-1=26