x = 9 / 4 - 1 / 10 : 2 / 5
x = 9 / 4 - 1 / 10 × 5 / 2
x = 9 / 4 - 1 / 4
x = 8 / 4
x = 2 ∈ N
x = 9/4 - 1/10 : 2/5 = 9/4 - 1/10 * 5/2 = 9/4 - 1/4 = (9 - 1)/4 =8/4 = 2