one book mass = 30 / 108
so (30/108) n = 20
n = 20 *108 /30
= (2/3)(108) = 2*36 = 72 books
108 identical books have a mass of 30kg what's the number of such books that have a mass of 20 kg
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2 answers
2/3 the mass, so 2/3 the books: 2/3 * 108 = 72
or, as a proportion,
x/20 = 108/30
x = 72
or, as a proportion,
x/20 = 108/30
x = 72
2 answers