Marlo's guess was 4 higher than the actual number of 80 marbles in the jar. To find the percent of error, we need to know what percent of 80 the error of 4

40 marbles divided by 10 results in the 4 marbles Error MArlo made, Divide 50% by 10 to see what the answer is :)

Right Hayley and if 50% is 40, we can assume that 5% would be 4? so the answer would most likley be 5%

Error is   4/80 x 100 = 5%   

Second Question:   If 80 marbles is 100%    50% is:   80 x.5 = 40 marbles