In the following ASCI structure (single bond under "$\ce{CH}$" containing $\ce{CH2,CH2, CH3}$)
$$ \begin{align*} \ce{CH3-CH2-CH2-&CH-CH3}\\ &|\\ \ce{&CH2-CH2-CH3} \end{align*} $$
The correct way to name it is "4-methlyheptane".
But when I do it the way I have been taught I get the following "4-propylpentane". Here are my systematic steps:
Firstly, I count the longest carbon chain. In this case its 5 carbons together so suffix -pentane. Then I look to see if there are any branched chains and number it from left to right. In this case the branched chain is on number 4. The branched chain contains $\ce{CH2-CH2-CH3}$, resp. $\ce{C3H7}$, aka propyl.
Ergo, 4-propylpentane, however, the correct answer as mentioned above is 4-methylheptane.
How is it 'heptane' ? The longest chain has FIVE carbons. I got the '4-' part correct, but how is $\ce{CH2-CH2-CH3}$ Methyl? Is this a mistake in my book?