PSLE Harry used 80 tacks to pin his flashcards side by side onto a board as shown. How many flashcards did he pin altogether?
1 Flashcard → 4 tacks = 2 + (1 x 2)
2 Flashcards → 6 tacks = 2 + (2 x 2)
Formula:
2 + (Flashcards x 2) = Number of tacks
2 + (Flashcards x 2) = 80
Flashcards x 2 = 80 - 2
Flashcards x 2 = 78
Number of flashcards that Harry pinned
= 78 ÷ 2
= 39
Answer: 39