person( 1 ) {had to DO|was assigned} PROBLEMS START through END for homework {{last {week|night}}|tonight}.
If person( 1 ) DID all of the PROBLEMS he( 1 ) was assigned, how many PROBLEMS did he( 1 ) DO?
ANSWER
Instead of counting PROBLEMS START through END, we can subtract START - 1 from each number so we instead consider PROBLEMS 1 through ANSWER.
We see that person( 1 ) DID ANSWER PROBLEMS.
Notice that he( 1 ) DID ANSWER and not ANSWER - 1 PROBLEMS.
A baker has a whole {baguette|loaf of bread}.
How many cuts must {he|she} make to have exactly NUM even slices?
NUM - 1
One cut will make two slices, two cuts will make three slices, and so on.
Therefore, we need NUM - 1 cuts to make NUM slices.
person( 1 ) is building a straight fence, with posts one meter apart.
If the fence is LENGTH meters long, how many fence posts does he( 1 ) need?
LENGTH + 1
If the fence is one meter long, he( 1 ) needs two posts (one for each end).
If the fence is two meters long, then he( 1 ) needs three posts, and so on.
Therefore, he( 1 ) needs LENGTH + 1 posts for a LENGTH meter fence.