Question

If 6+4=210 then ?+?? =123 how

Answer 1

if we apply a logic here 
if we divide the r.h.s into 2 parts
the first part is the subtraction of the 2 numbers and 2nd part is the addition of the 2 numbers
6-4=2,6+4=10
so,it is like a+b=(a-b),(a+b)
in eq (2)
c-d=1,c+d=23
by solving the above equations we get
2c=24
c=12
d=11
hope it helps...!!!! 

Answer 2

You see, you have to apply the formula
a + b = ( a - b) ( a + b)
6 + 4 = ( 6 - 4) ( 6 + 4) = 210

Similarly, Let the two unknown numbers be x and y
x+ y = ( x - y) ( x + y)
x + y = 123

x- y = 1 .....(i)
x + y = 23.......(ii)

Solving both equation (i) and (ii),
2x = 24
x = 12

Putting the value of x = 12 in equation (i),
12 - y = 1
y = 13

So , 12 + 13 = 123