I'll Give u the right way to do this
First of all u will need :
1- Pen & Paper
2- Calculator
And do this :
1- Write the two given numbers and the number between .. For Example : The Numbers are 7 & 9 , u Must write 8 beside them on the note
do that with all Five Given Numbers till u have something like this
7 9 8
7 9 8
1 3 2
4 6 5
7 9 8
2- Bring ur calculator ( it's the toughest part ) , then try to calculate a number from each column , For Example : 7+9+2+6+7= 31
if this number wasn't right he will tell u that this number is Less\More Than the actual number , For Example He told u that the number is More Than the Number , Calculate the numbers again Lets say : 7+7+2+4+7= 27 TRY IT!
and he will tell u that the number is Less than the actual numbers if it wasn't right
So the number lies between 31 and 27 So the number will be 30 , 29 , 28
and one of them is the right Number
It's Looks hard but its alot fun