Olivia uses the work below to determine 55% of 720.

Question

Step 1: 
Step 2: 50% of 720 =  = 360
           10% of 720 =  = 72
             of 720) =  = 31
Step 3: 360 + 72 – 31 = 401

Which explains the error in Olivia’s solution?

Step 1: Olivia used percents that are not equivalent to 55%.

Step 2: Olivia incorrectly determined 50% of 720.

Step 2: Olivia incorrectly determined  of 10% of 720.

Step 3: Olivia subtracted  of 10% when she should have added.

Answer 1

55/100*720=55*72/10=11*72/2=11*36=396.

55=50+5. 50% is 1/2 and 5%=1/20. 1/2 of 720=360; 1/20 of 720=36, and 360+36=396. Step 2 was wrong because 1/2 of 72=36, not 31. Answer 3.