2012/8/4 ZulTan <zul_...@yahoo.com> > Assalamu'alaikum warahmatullaahi wabarakaatuhu, >
Wa'alaykumus salaam warahmatullahi wabarakaatuh, > Problem 1: > A boat travels 12 km upstream and back in 1 hour 45 minutes. > If the speed of the current is 3 km/h throughout, find the speed of the > boat in still water, giving your answer correct to 3 significant figures. > s = 12 km t = 1.75 h 12 / (v - 3) + 12 / (v + 3) = 1.75 (12(v+3) + 12(v-3))/(v^2 - 9) = 1.75 12(v+3) + 12(v-3) - 1.75(v^2 - 9) = 0 12v + 36 + 12v - 36 - 1.75v^2 + 15.75 = 0 - 1,75v^2 + 24v + 15,75 = 0 v = 14.342 km/h > Problem 2: > A motorist makes a journey of 240 km from Singapore to Malacca to visit > his in-law at an average speed of X km/h. Write down an expression for the > number of hours taken for the journey. > t1 = 240/X hour > On his return jouney from Malacca to Singapore, his average speed is > reduced by 6 km/h due to heavy traffic at the causeway. Write down an > expression for the time taken for the return journey. > t2 = 240/(X - 6) hour > If the return journey takes 20 minutes longer, from an equation in X and > solve it to find the average speed for each journey, giving your answer > corret to two decimal places. > t2 = t1 + 1/3 hour 240/(X - 6) = 240/X + 1/3 720X - 4320 + X^2 - 6X - 720X = 0 X^2 - 6X - 4320 = 0 X = 68.80 X1 = X = 68.80 X2 = X - 6 = 62.80 Nice to have argumentation of mathematical nature, instead of ad populum and ad verecundiam ones. Thank you, Pak ZulTan. -- Abu 'Abdirrahman, Ahmad Ridha bin Zainal Arifin bin Muhammad Hamim (l. 1400 H/1980 M) -- -- . * Posting yg berasal dari Palanta RantauNet, dipublikasikan di tempat lain wajib mencantumkan sumber: ~dari Palanta R@ntauNet http://groups.google.com/group/RantauNet/~ * Isi email, menjadi tanggung jawab pengirim email. =========================================================== UNTUK DIPERHATIKAN, melanggar akan dimoderasi: - DILARANG: 1. E-mail besar dari 200KB; 2. E-mail attachment, tawarkan di sini & kirim melalui jalur pribadi; 3. One Liner. - Anggota WAJIB mematuhi peraturan serta mengirim biodata! Lihat di: http://forum.rantaunet.org/showthread.php?tid=1 - Tulis Nama, Umur & Lokasi disetiap posting - Hapus footer & seluruh bagian tdk perlu dlm melakukan reply - Untuk topik/subjek baru buat email baru, tdk mereply email lama & mengganti subjeknya. =========================================================== Berhenti, bergabung kembali, mengubah konfigurasi/setting keanggotaan di: http://groups.google.com/group/RantauNet/
