Three numbers are in the ratio 3:9:10. If 10 is added to the last number, then the three numbers form an arithmetic progression. What are the three numbers?

The numbers are 6, 18, and 30

Step-by-step explanation:

If the three numbers are in the ratio of 3:9:10,

let the numbers be 3x, 9x and 10x.

If 10 is added to the last number to form an arithmetic progression

Then, 3x 9x (10x+10) are the progression

The common difference of an arithmetic progression (d) = T₂ - T₁ = T₃ - T₂

T₂-T₁ = T₃ - T₂ ... Equation 1

Where T₁ = first term of the progression, T₂ = Second term of the progression, T₃ = third term of the progression

Given: T₁ = 3x, T₂ = 9x, T₃ = 10x + 10

Substituting these values into equation 1

9x-3x = (10x+10) - 9x

Solving the equation above,

3x = 10+x

3x-x = 10

2x = 10

x = 10/2

x = 2.

Therefore the numbers are 6, 18, and 30