PSLE Bobby used 42 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) = 42
Flashcards x 2 = 42 - 2
Flashcards x 2 = 40
Number of flashcards that Bobby pinned
= 40 ÷ 2
= 20
Answer: 20