I g ia th iet (dieu �i�n) n a o d 6 kh6 ng. toa n, t a g i a s u h a y kho n g c6 tron g dieu ki�n da c h o cua ba i toa n . Bva vao g i a th i et d6 CLing voi n h un g dieu ki�n da cho c u a bai to a n de de d a n g tl m ra each g ia i cua ba i toa n . Day I a g ia thiet c6 y n g hia t� m thai v a dap s 6 bai toan kh 6ng ph� t hu¢c vao g i a thiet d6. VI d � 1 : Q uyt n g on moi qua c hia ba Ca m n g o n mo i qua c h i a ra l a m m voi M o i n g voi m c)t mh�ng, tra m n g voi C6 1 7 qua kh 6 n g n h ieu du ch i a H o i co ba o n h i eu q ua ca m, bao n h i e u q ua q u yt? Bai la m : Gia s ir tat ca 1 7 q ua deu Ia cam thl c6 s 6 ph an fa: 1 7 x 7 0 = 1 70 (phan) 56 ph an dura Ia: 1 70 - 1 00 = 70 (phon) Mol/an thay mgt qua quyt bang m¢t qua cam thi s6 ph an tang them Ia: 1 o - 3 = 1 (phanJ so qua q uyt Ia: 10 : 1 = 1 o (qua) S6 quii cam Ia: 1 7 - 1 0 = 7 (qua) Vi d\1 2: Dap so : 7 qua cam, 1 o qua quyt Be d�t ong da n n ubc tren m<)t do 9 n auO'ng c6 the d u n g 70 o n g dai h o�c 1 20 6 n g n ga n N h lin g do d u n g ca h a i l o�i n e n d u n g h et tat ca 90 o n g . Tfn h so o n g . m o i IOS� i. Mot 1 : 70 . 6ng do; lap duoc: . = 1 (doan auetng) . 70 Mot 1 : 7 20 = -1- (aoan . ong ngan lap dude: . . au'Cing) 1 20 Arc h i m edes School Aschool.edu_vn I 3 ARCH I MEDES SCHOOL Toa n s - Quyen 4.1 Gia su 90 ong deu la logi dai. Khi a6 sophan aoan 1 = � (aoan au'ong) au'on g lap au'dc . la: 90 X 70 � £Joan auong dti ra Ia: 9 - 1 = .� (ao n aLian g) Moi Jan thay m(Jt 6ng ngan bang m¢t 6ng dai, OOt;In attong tang them Ia: 1 - _l_ = 1 (aoQn auong) 70 1 20 1 68 . ..t ,� 2 1 "' "" · r' So ong ngan a: - : - = 4B tong ) 7 1 68 Biti 1 0. B�n Blnh chi a 79 vi<�n bi tha nh 1 2 nh6m sao cho moi n h6m c6 s6 bi khac n ha u . Hoi nh 6 m c6 so bi n hiE�u n hat c6 bao n h ieu vi en? Bai 1 1. B�n An ch�y qua n h , m9t san v�n d¢n g hl.n h c h t1 n h�t c6 c h i eu r¢ng Ia SOm; c h ieu dai Ia 7 1 ,sm va h a i n U'a hlnh tron nhv hl r:th ve.