Choose a 3 digit number whose first and last digits differ by at least 2.

E.g 853

Reverse this number

I.e. 358

Subtract the smaller from the larger

I.e. 853 – 358 = 495

Add this number to the reverse of this number

I.e. 495 + 594 = 1089

Why? (That’s the fascinating part of maths.)

Thanks to Alex Bellos’s book “Alex’s Adventures in Numberland” for rekindling my interest in numbers.

My demonstration of why 1089 is the answer:

	hundreds	tens	units	notes
start	a	b	c	a>c+1
invert	c	b	a
subtract	a-(c+1)	10+b-(b+1)	10+c-a	+10 carry 1 in tens,units
simplify		9
invert	10+c-a	9	a-(c+1)
add	10	8	9	Carry 1 in tens