Diketahui a : b = ( 2r- 1) : 20, nilai p = 60 dan q = 45.jika a : b berbalik harga dengan p : q, maka nilai r

[tex] \frac{a}{b} = \frac{q}{p} \\ \frac{2r - 1}{20} = \frac{45}{60} \\ 60(2r - 1) = 20 \times 45 \\ 120r - 60 = 900 \\ 120r = 900 + 60 \\ 120r = 960 \\ r = \frac{960}{120} \\ r = 8[/tex]