Question

100×10-(100-2×x-60)×10=900

Answer 1

100 × 10 - ( 100 - 2 × X - 60 ) × 10 = 900

1 000 - ( 100 - 2 × X - 60 ) × 10 = 900

( 100 - 2 × X - 60 ) × 10 = 1 000 - 900

( 100 - 2 × X - 60 ) × 10 = 100

100 - 2 × X  - 60 = 100 : 10

100 - 2 × X = 10 + 60

2 × X = 100 - 70

2 × X = 30

X = 30 : 2

X = 15 → numarul, aflat prin metoda mersului invers

Verific:

1 000 - ( 100 - 2 × 15 - 60 ) × 10 = 1 000 - 10 × 10 = 900