Question

media aritmetică a 7 nr impare consecutive este 15 , atunci care e cel mai mare ?

Answer 1

Ma = [ a + (a+2) + (a+4) + ( a+6) + ( a+8) + ( a+10)+ (a+12)] : 7 = 15
⇒ a + (a+2) + (a+4) + ( a+6) + ( a+8) + ( a+10)+ (a+12) = 7 ×15 =105
7a = 105 - 42
7a=63 ⇒ a = 63 : 7 ⇒ a = 9  → primul numar
9 + 12 = 21 → numarul cel mare 

verific : (9+11+13+15+17+19+21) : 7 = 105 : 7 =15 ( Ma)

Answer 2

[x+(x+2)+(x+4)+(x+6)+(x+8)+(x+10)+(x+12)]÷7=15
→x+(x+2)+(x+4)+(x+6)+(x+8)+(x+10)+(x+12)=7×15=105
7x=105-42
7x=63→x=63÷7→x=9⇒primul nr.
9+12=21⇒nr. cel mare

Verificare:

(9+11+13+15+17+19+21)÷7=105÷7=15