Question

[(15x6-10x3xa)x4+15x4]x10=30x100

Answer 1

[ ( 15 × 6 - 10 × 3 × a ) × 4 + 15 × 4 ] × 10 = 30 × 100

[ ( 90 - 30 × a ) × 4 + 60 ] × 10 = 3 000

( 90 - 30 × a ) × 4 + 60 = 3 000 : 10

( 90 - 30 × a ) × 4 + 60 = 300

( 90 - 30 × a ) × 4 = 300 - 60

( 90 - 30 × a ) × 4 = 240

90 - 30 × a = 240 : 4

90 - 30 × a = 60

30 × a = 90 - 60

30 × a = 30

a = 30 : 30

a = 1 → numarul, aflat prin metoda mersului invers

Answer 2

[(15x6-10x3xa)x4+15x4]x10=3000
(90-30xa)x4+60=3000:10=300
(90-30xa)x4=300-60=240
90-30xa=240:4=60
30xa=90-60=30
30xa=30
a=30:30
a=1

Sper că te-am ajutat! :)