Binary addition and subtraction with X=10111, Y=101, Z=1001

[rclakmal]

Obtain Binary String ?

Homework Statement

Given That X=10111 ,Y=101; Z=1001, obtain binary strings that represent P Q where
P=X+Y and Q=P-Z; state clearly each rule you apply .

Homework Equations

The Attempt at a Solution

Hey up to the extent which i know i did this as a normal binary addition and subtractions >then i got P=10010
and Q=1001 .But the problem is I am not sure that i have used any kind of rules here. or Have I ?? Or did i made a mistake in interpreting the problem .Can somebody help . this is all u got for that question ,i have included all the details.

 

[Mark44]

Doing binary addition, I get a different result for P. The addition rules in binary are:
0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 10

I can't think of any rules other than these.

So for X + Y you have
10111
+ 101
-----
11100