posted by Shawna Lynn .
Solve the mathematical puzzle.
Determine the digits of R from these clues.
The first digit is the answer when the third digit is divided by 2.
The second and third digits add to 7.
The second digit minus the first digit is 1.
R is a three-digit number: ____
I have never understood how to do this.
Call the digits a,b,c left-to-right
a = c/2
b+c = 7
b-a = 1
we see that c=2a, so
subtract to get
Thus c=4 and b=3
Or, just working with the specs,
c must be even, since it can be divided by 2. So, R is one of the forms
Since the last two add to 7, R must be