Answer :

1) 3/4 - 1/2 = 3/4 - 2/4 = 1/4. Vanessa's brothers ate half of the cake. 

2) 1.75 + 2.4 = 4.15.  6.5 - 4.15 = 2.35.  4.15 = 2.35 = 1.8.  Chad hiked 1.8 ore miles in the morning than in the afternoon.