Question

4 caiete si 6 creioane costa 26 de lei. 2 caiete si un creion costa 11 lei. Cat costa impreuna un caiet si un creion?

Answer 1

a=caiete
b=creioane
4a+6b=26
2a+b=11
a+b=?
$2a+b=11$⇒$2a=11-b$⇒$a= \frac{11-b}{2}$
$4a+6b=26$⇒$4* \frac{11-b}{2} +6b=26$⇒$2* (11-b) +6b=26$⇒$22-2b +6b=26$⇒$4b=26-22$⇒$4b=4$⇒$b= \frac{4}{4} =1$
$a= \frac{11-b}{2}$⇒$a= \frac{11-1}{2}$⇒$a= \frac{10}{2} =5$
a+b=5+1=6
1caiet + 1creion = 6 lei