Reading Incomprehension

On Dan Hamermesh‘s always-interesting blog, I read the first sentence of a recent entry:

My grandson will be 13 in 13 months.

I had to read it three times to realize that this was not a clever way of saying that he had a brand new grandson. The “months” at the end of the sentence tied to the second “13,” combined with the word “grandson” (baby image comes to mind) conspired to persuade me that there should have been a “months” following the first “13” as well. How easily the mind — at least, mine — is tricked.

It reminds me of the following very easy math question that a lot of relatively smart people get wrong:

A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

A. $1.10
B. $0.10
C. $0.05
D. $1.00
E. $0.15

Hint: the answer is not B.