Guess #1: 3 science fiction novels and 1 mystery novel
Find the number of books:
3 + 1 = 4
Find the total cost in dollars:
(9 × 3) + (2 × 1) = 27 + 2 = 29
The guess is incorrect. Try another guess.
Guess #2: 2 science fiction novels and 2 mystery novels
Find the number of books:
2 + 2 = 4
Find the total cost in dollars:
(9 × 2) + (2 × 2) = 18 + 4 = 22
The guess is incorrect. Try another guess.
Guess #3: 1 science fiction novel and 3 mystery novels
Find the number of books:
1 + 3 = 4
Find the total cost in dollars:
(9 × 1) + (2 × 3) = 9 + 6 = 15
The guess is correct. Uncle Porter bought 1 science fiction novel and 3 mystery novels.