Mrs Koh baked 68 cookies on Monday. She baked 3/8 of the remaining cookies on Tuesday and the rest of the cookies on Wednesday. If she baked 65 cookies on Wednesday, how many cookies did she bake in the 3 days altogether?
Cal N the total number baked
Monday she baked 68
Tuesday she baked (3/8)(N - 68)
Wed she baked 65
So
68 + (3/8)(N -68) + 65 = N
133 + (3/8)N - (3/8)(68) = N rearrange as
133 - 25.5 = (5/8)N
107.5 = (5/8)N
N = 107.5 ( 8/5) = 172
+113 
