# Simple Arithmetic Puzzle 8. Or is it?

This one's different to all the previous ones...

\begin{align}7+53&=28\\16+6&=21\\5+19&=97\\15+8&=\,?\end{align}

Can you find the value of the question mark?

• I found something interesting. Let's represent your equations as $A+B=C$. Let $A\| B$ mean "A concatenate B" and $d(x)$ be the "digits of some assigned $x$". Also, let $n$ be the number that corresponds to the position of each equation ($n=1$ for first equation, $n=2$ for second equation, etc) then for some value $D$, if $$D=\frac{A\| B-d(A)\cdot d(B)}{\frac{1}{2}|A - B|+2-n}$$ then $D$ is an integer, and close to $C$ :) – Feeds Jul 6 at 6:46

84

step1

convert all numbers to chemical element symbol

step2:

concatenate them to get R.H.S.

step3:

convert result to atomic number

e.g.

7+53=N+I=Ni=28
16+6=S+C=Sc=21
5+19=B+K=Bk=97

• 16+92+15+68+5... – Ak19 Jul 3 at 12:03