# Thread: The sum on two numbers in 28...

1. ## The sum on two numbers in 28...

The sum of two numbers is 28 and their product is seven. Find the sum of the reciprocals of the numbers.

This one has me confused. How can their product equal 7 if 7 is prime?
1+27 027 14+14 196
2+26 052 13+15 195
3+25 075

2. This is just a very basic algebra problem.
x+y=28
xy=7

(1/x)+(1/y)=?

3. Hello, ceasar!

The sum of two numbers is 28 and their product is seven.
Find the sum of the reciprocals of the numbers.

This one has me confused.
How can their product equal 7 if 7 is prime?
WHO said these are whole numbers ??
There is a marvelously sneaky trick for this one . . .

We have: .x + y .= .28 . [1]
. . . . . . . . .xy . = . .7 . .[2]

Divide [1] by [2]: . x + y . . .28
. . . . . . . . . . . . . ------- .= .---
. . . . . . . . . . . . . . .xy . . . . 7

. . . . . . . . . . . x . . .y
And we have: .--- + --- .= .4
. . . . . . . . . . .xy . . xy

- - - . . . . . .1 . . 1
Therefore: - -- + -- .= .4 . . . . ta-DAA!
- - - . . . . . .y . . x

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### what topic is this mathematics: find the product of two numbers that is equal to 195

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