Răspuns:
6.
315 Lei
7.
450 sticle
8.
Explicație pas cu pas:
ex 6
notam suma totala ( pretul bicicletei) cu S
1a luna economiseste 1/7 S
a 2-a luna economiseste 2/6 ( S-1/7S)
a-3 aluna economiseste 3/5 [ S- 1/7S- 2/6(S-1/7S)]
a 4-a luna economisste 72 Lei
suma economiilor din cele patru luni =- pretul bicicletei , adica:
S x (1/7 ) + 2/6 x [S - S x (1/7)] + 3/5 x { S- S x (1/7) - 2/6 x [S-S x (1/7)] } + 72 =S
S/7 + 2/6 x [ (7 x S -S)/ 7 ] + 3/5 x { S- S/7 - 2/6 x [ (7S-S)/ 7 ] } +72 = S
S/7 + 2/6 x 6S/7 + 3/5 x ( S-S/7- 2/6 X 6S/7 ) +72= S
S/7 + 2S/7 + 3/5 x [(7S-S -2S)/7 ] + 72 = S
3 S/ 7 + 3/5 x 4S/7 + 72 = S
(15 S +12 S)/35 +72 = S
(27 S + 72 x 35)/35 = S
27 S + 2520= 35 S
35S-27S= 8 S = 2520 rezulta S = 2520/8= 315 Lei
ex 7
Notam cantitatea totala de apa (in sticle) C
prin urmare putem scrie ca
C- ce s-a vandut in cele trei zile = 58 sticle
adica,
C- 1/2 x C- 2/3 x ( C-1/2 x C) -17= 58
(2 xC - C )/2 - 2/3 x [( 2C-C)/2] - 17 = 58
C/2 - 2/3 x (C/2) -17 = 58
C/2- C/3-17=58
aducem la acelasi numitor 6 in partea stanga:
3 C /6 - 2C/6 -17 = 58
(C- 17 x 6)/6= 58
C-102 = 58 X6 = 348
c= 348+102= 450
