I found this question on my boy's paper :
If @ + # = 12, @ - # = 4. Find out the value of @ #.
He is in primary one and I thought it would be rather hard on a little boy who has just been inducted to the primary school system to solve this problem. So I thought hard of a way to help him with it.
I used the first equation: @+#= 12. With that, I asked him to list all the possible combination. So he wrote:
6+6, 7+5, 8+4, 9+3, 10+2, and 11+1.
I nodded approvingly and ask him which of the combination proves the second equation: @-#=4 correct.
He thought hard and needed a bit more coaching as we worked all the possible combinations together.
Finally, he deduced that only the 8+4 equation corresponds to the answer. So, he deduce that @ + 8 and # = 4!!
I gave him a few more of such practices before he perfected the art, but I must say, it was worth the while! ;)