Each letter in the equation below represents a different digit from the set {1,3,4,7,8}. Find the value of each letter to make the equation true.

Question

ADD
+MAD
_____
SUM

Answer 1

This is quite straight forward if taken stepwise. There are only 5 possible values which are given in the question. Start with D and work through the values. D+D=M
If D=1 M can't = 2 (2 is not a possible value)
If D=3 M can't = 6
if D=4 M=8
if D=7 M=4
if D=8 M can't =6

So we now only have two possible values for D, D=4 or D=7.

Start with D=4. If D=4 then M=8. But A+M<10 as the total of the sum is less than 1000. So A can only =1. But if A=1 then U=5 which is not possible as 5 is not in the list of possible values. So D can't =4

This leaves us with D=7. so the sum is now:

A77
+4A7
_____
SU4

Can you take from here?