$c, X × 40 × 25 = 2000$
$⇒ X × 1000 = 2000$
$⇒ X = 2$
$Vậy$ $X = 2$
$d,( X × 40) × 25 = 2000$
$⇒ X × 40 × 25 = 2000$
$⇒ X × 1000 = 2000$
$⇒ X = 2$
$Vậy$ $X = 2$
$e,( X – 10 ) × 5 = 100 - 20 ×4$
$⇒ x -10 = 20 ÷ 5$
$⇒ x - 10 = 4$
$⇒ x = 14$
$Vậy$ $X = 14$
$g, ( X + 2) + ( X + 4 ) + …+ ( X + 1996) = 998000$
$⇒ (x +x +...+x) + (2 +4 +...+1996) = 998000$
$⇒ 998x + \frac{(2 +1996).998}{2} = 998000$
$⇒ 998x + 997002 = 998000$
$⇒ 998x = 998$
$⇒ X = 1$
$Vậy$ $x = 1$