Paula wants to arrange a math book, a Portuguese book, an English book, a computer book and a geography book side by side on her bookshelf. Knowing that the math and Portuguese books should always be together, determine how many different ways Paula can arrange the books.
A) 48
B) 24
C) 12
D) 7
E) 5
Solution in that question we can use an artificiality:
I gonna considered the book of mathematic as one book but here we gonna remember that the mathematic book only could be near of the one of protuguese but it can be at the left or the right in order, so after find the result I gonna multiply by 2, easy like that and I gonna use to the solution the same formula for anagrams that I taught yesterday, 1- mathematic, Portuguese, 2 - English, 3 - information, 4 - geography.
so we have 4 books because two only could be near each other 3 places, imagine you thinking that is the formula for two symbols that are the same and isn't thanks God I am here to explain to you,
So we have the big book, the English, information, and geography that are 3 places and the multiplying the 4x3x2 = 12, but the book of mathematic need be near the one of Portuguese but can swap and be at left or right of the other so let's multiply by 2 that is 12x2 = 24.
Is better be intelligent than invent a formula doesn't you agree? And Rute if was 3 books no matter is a big book that in the end can swap the 3 places so you so in the end you gonna multiply the anagram by the big number-book-symbol-letter by it permutation that for 3 is 3x2x1 = 6, so is better than invent a formula is just think about.
Rute Bezerra de Menezes Gondim
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