<PRE><B>Question 135924</B>

Let x=the tens digit
Ane let y=the units digit

Now we are told that:

x=2y---------------------------eq1

The sum of its digits is x+y and the number is 10x+y, ok?
And we are being told that:

(x+y)(10x+y)=63  using the FOIL (First, Outer, Inner, Last) crutch we get:

10x^2+xy+10xy+y^2=63 and this equals
10x^2+11xy+y^2=63--------------------------eq2

substitute x=2y from eq1 into eq2
10(2y)^2+11(2y)(y)+y^2=63 simplify

40y^2+22y^2+y^2=63  collect like terms

63y^2=63  divide each side by 63

y^2=1  take square root of each side
y=+ or - 1 so
y=+1
and y=-1
And substituting these into eq1, we get:
x=+2, when y=+1
and
x=-2, when y=-1

So our answer is +21

CK
Lets look at +21  
2 is twice 1 so first condition is met; if the number is multiplied by the sum of its digits, the result is 63---3*21 is 63 so the second condition is met 


Hope this helps---ptaylor











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