Two numbers differ by `3`. The sum of the greater number and twice the smaller number is `15`. Find the smaller number.

Explanation

Let the greater number be `x` and the smaller number by `y`.
From the first condition, `x-y=3`……`(1)`
Twice the smaller number `=2y`
From the second condition, `x+2y=15`……`(2)`
We want to find the smaller number.
`:.` eliminate `x`.
Subtracting equation `(1)` from equation `(2)`.
`{:(x+2y=15" ...(2)"),(x-y=3" ...(1)"),("- + -"),(bar(""3y""=" "12")):}`
`:.y=(12)/(3)` `:.y=4`.