Question

Un automobil a parcurs o distanta in trei zile astfel: in prima zi a parcurs 7 supra 20 din drum,a doua zi a parcurs 1 supra 5 din distanta ramasa, iar a treia zi a parcurs restul de 624 km.

a) Cati km are intreaga distanta?
b) Cati km a parcurs automobilul a doua zi? 

Answer 1

x-lungimea drumului

7/20 din x=  7/20 *x =   7x/20 - prima data

x-7x/20=  (20x-7x)/20=  13x/20 -restul

1/5 din 13x/20=  1/5 * 13x/20=  13x/100 -a doua oara

13x/20 -13x/100= (65x-13x)/100=  52x/100 -noul rest

52x/100=624

x=100*624/52

x=100*12

x=1200

13*1200/100= 13*12=  156 a parcurs a doua oara

Answer 2

Notezi toata distanta drumulului cu x
deci x= I +II+ III
prima zi I=7/20 *x
a doua zi II=1/5(x-I)= 1/5(x-7/20*x)
  a treia zi III=624 km
=> x= 7/20*x +1/5 (x-7/20 *x) +624 
aducem la acelasi numitor si avem (numitor comn 100)
 100x=35x+20x-7x+62400
100x=55x-7x+62400
100x=48x+62400
100x-48x=62400
52x=62400
x=62400/52
x=1200 km 
I= 7/20 *1200=420 km in prima zi
II=1200-420-624=156 km in a doua zi