Answer: Keith's budget deficit by $3.75.
Step-by-step explanation: Given that Keith wants to buy an address book that costs $5.00, but he has only $1.25 in his budget.
We are to calculate the deficiency in his budget.
Cost price of the book = $5.00.
And, Keith's budget = $1.25.
So, the cost of the book is greater than Keith's budget.
Therefore, the deficiency in Keith's budget is given by

Thus, Keith's budget deficit by $3.75.