How do you find two consecutive positive odd integers whose product is 143?

3 Answers
Feb 6, 2016

143 = 11 xx 13

Explanation:

Notice that consecutive odd integers will differ by 2, so we could call the even number between them n, making the two integers n-1 and n+1.

So:

143 = (n-1)(n+1) = n^2-1

Add 1 to both ends and transpose to get:

n^2 = 144 = 12^2

So n = +-12

Since we are told that the integers are positive, use n=12 to find the pair of integers: 11, 13.

Alternatively, just find factors of 143, trying prime numbers in turn: 2 (no), 3 (no), 5 (no), 7 (no), 11 (yes). Then 143/11 = 13 - we have found our pair of numbers.

Feb 6, 2016

11 and 13

Explanation:

Proceed as below.
Let (2n+1) be the first odd integer, where n is any positive integer. Second number being consecutive is (2n+3)
Rest of the steps are same as followed by others.

It is by convention, as 2n+1 is always odd.

Feb 6, 2016

Expanding on AO8's answer: This approach guarantees that any number we look at is odd:" "Solution: 11 & 13

Explanation:

We need to be able to guarantee that we are dealing with odd numbers.

Let n be any number where n>0

Suppose n is even. Then 2n is also even.
Suppose n is odd. Then 2n is also even.

But in both cases 2n+1 will be odd.

Let the first odd number be 2n+1
Then the second odd number will be 2n+3

We are given that the product is 143 so write the equation as:

(2n+1)(2n+3)=143

This is saying exactly the same thing as the others but in a slightly different way! So we now have:

4n^2+8n-140=0

Divide by 4

n^2+2n-35" "=" "(n+7)(n-5)" "=" "0

So for my conditions n=-7" or "+5

n=-7" does not work so we use " n=5

Thus the first number is: (2n+1)" "->" "2(5)+1=11

So the second number is 11+2=13