Let P = pencil length, M = marker length and Pn = pen length.
We know that the sum of these lengths is 48 cm so:
P + Pn + M = 48 (Equation 1)
Now we need to use the relationships of the lengths to find 2 more equations:
Pn = M - 1 (Equation 2)
M = P - 1 (Equation 3)
Now, sub Equations 2 and 3 into the first equation and solve for the value of P, which is 17.
Next, use the value of P to find your M value and then finally use that M value to get your Pn value.
The final answer is: pencil length = 17cm, marker length = 16cm and pen length = 15cm.