Question

cunoacand faptul ca 3 stilouri si 5 penare costa 225 lei iar 3 stilouri si 2 penare costa 135 lei aflati cat costa un stilou
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Answer 1

s-stilouri

p-penare

3s+5p=225

3s+2p=135

.........................

/      3p=90

p=90:3

p=30

3s+2 x 30=135

3s=135-60

3s=75

s=75 : 3

s=25

Un stilou costa 25 lei .

Answer 2

$3s + 5p = 225 \\ 3s + 2p = 135$

$scadem \: cele \: doua \: relatii \: si \: obtinem \: \\ 3s + 5p - 3s - 2p = 225 - 135$

$3p = 90 \\ p = 30 \: lei$

$s = \frac{225 - 150}{3} = \frac{75}{3} = 25 \: lei$