The total length of pencils A, B and C is 29 cm. Pencil A is 11 cm shorter than pencil B, and pencil B is twice as long as pencil C. How long is pencil A?

Let B = L

Let A = L - 11

Let C = (1/2)B = (1/2)L = .5L

So we have that

A + B + C = 29

(L -11) + L + (.5)L = 29 simplify

2.5L - 11 = 29 add 11 to both sides

2.5L = 40 divide both sides by 2.5

L = 16

A = L - 11 = 16 - 11 = 5 cm