To find Bob's original pay before the 5% increase, we can set up the equation as follows:

Let $x$ represent Bob's original pay. After the 5% increase, his new pay is $315. This means his original pay plus 5% of his original pay equals $315:

$x + 0.05x = 315$

This simplifies to:

$1.05x = 315$

Now, solve for $x$:

$x = \frac{315}{1.05}$

$x = 300$

So, Bob's original pay was $300.

Would you like more details or have any questions?

Here are 5 related questions to expand on this:

1. What would Bob's pay be if his pay increased by 10% instead of 5%?
2. If Bob's pay decreased by 5%, what would his new pay be?
3. How much did Bob's pay increase in actual dollars?
4. If Bob's pay increased to $400 after a 5% raise, what was his original pay?
5. What would Bob's original pay be if the final amount was $315 after a 7% increase?

Tip: When solving percentage problems, it's often easier to convert percentages to decimals (e.g., 5% = 0.05) for use in equations.