If a watch costs $40 and you must pay 6.5 % sales tax, how much will the tax be?

To calculate the sales tax on a watch that costs $40 with a tax rate of 6.5%, you can use the following formula:

\[ \text{Sales Tax} = \text{Cost} \times \text{Tax Rate} \]

Substituting in the values:

\[ \text{Sales Tax} = 40 \times 0.065 \]

Calculating that gives:

\[ \text{Sales Tax} = 2.60 \]

So, the sales tax will be $2.60.