A math problem 5x + 2.5x = 15

A math problem 5x + 2.5x = 15

5x+2.5x=15
7.5 x = 15
x = 15 ÷ 7.5
x = 2

A mathematical problem, 5x-4 / x + 1 = 5 (x + 1) - 9 / X-1 = 5 (x + 1) / x + 1-9 / x + 1 = 5-9 / x + 1
Following the idea of solving this problem, x ^ 2-3x + 1 / x + 2 is transformed into the sum of an integral and a fraction, and the number of the numerator is less than that of the denominator

[x^2-3x+1]/[x+2]
= [(x+2)^2 -7x -3] / [x+2]
= [(x+2)(x-5) +11] / [x+2]
= x-5 + 11/(x+2)

2 (5x-4) - 3 (x + 6) = 5 (x-1) - x for X

10x-8-3x-18=5x-5-x
10x-3x-5x+x=-5+8+18
3x=21
x=7

A math problem 55
If the natural number n makes the vertical addition n + (n + 1) + (n + 2) do not produce carry phenomenon, then n is called "continuous number". For example, 12 is continuous number, because 12 + 13 + 14 does not produce carry phenomenon, but 13 is not continuous number, then how many continuous numbers are less than 1000?

Single digit: 3
Tens: 3 * 3 = 9
Hundreds: 3 * 4 * 3 = 36
Total: 3 + 9 + 36 = 48