Risma membeli 2 pulpen dan 1 buku tulis seharga Rp15.000, sedangkan Andika membeli 1 pulpen dan 2 buku tulis seharga Rp18.000. Jika Gina membeli 5 pulpen dan 3 buku tulis, berapa ia harus membayarnya?

<p>misal:</p><p>p=pulpen<br>b=buku tulis<br><br>2p+ b=15.000 &nbsp;--&gt; &nbsp;b=15.000-2p.....(1)</p><p>&nbsp;p+2b=18.000.....(2)</p><p>&nbsp;</p><p>substitusi persamaan 1 ke persamaan ke 2</p><p>&nbsp;</p><p>p+2(15.000-2p)= 18.000</p><p>p+30.000-4p &nbsp; &nbsp; = 18.000</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; -3p &nbsp;= 18.000-30.000</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; p &nbsp;= 12.000 / 3&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 4.000</p><p>cari nilai b : substitusi nilai p ke persamaan 1</p><p>b= 15.000-2p</p><p>&nbsp; &nbsp;= 15.000-2(4.000)</p><p>&nbsp; &nbsp;= 15.000-8.000</p><p>&nbsp; &nbsp;= 7.000</p><p>&nbsp;</p><p>Gina membeli 5p+3b = 5(4.000)+3(7.000)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;=20.000+21.000</p><p>Gina harus membayar &nbsp;Rp 41.000</p><p>&nbsp;</p>