Sum of observations (numbers) =5+6+7+x Total number of observations (numbers) = how many numbers are in the observation. In this case 4, thus (5,6,7 and x ) Every number is divisible by 1 Re-write the equation Simplify like terms and cross multiply to solve for the value of x 1×(18+x)=4×8 1 times any number is the same number, hence 1x(18+x)=18+x 4×8=32 18+x=32 x=32−18 x=14