A certain hobby shop sold model cars for $5.00 each and model trains for $8.00 each. If a customer purchased both cars and trains from the store for a total of $31.00, what total number of cars and trains did the customer purchase?
Choices:
A) 3
B) 4
C) 5
D) 6
E) 7

Rationale: we can take numbers , as price of car 5 , 8 for train and 31 total for ease . now we can determine quickly that total number should range between 31 / 8 < = n < = 31 / 5 , so ans should be between 3 and 7 . now solving the expression 5 a + 8 b = 31 decreasing 31 in multiple of 5 and checking divisibility of that number by 8 . this way we get 3 cars , 2 trains we get $ 31.00 total 3 * 5 + 2 * 8 = 31 hence total number is 3 + 2 = 5 ans c
Answer: C