A product is sold for $240 after a 20% discount. What was the original price?

A 20% discount means the selling price is $100\% - 20\% = 80\%$ of the original price.

Let $P$ be the original price. $0.80 \times P = \$240$

$P = \frac{\$240}{0.80}$ $P = \$300$ The original price was \boxed{\text{\300}}$.

Q2) If 5 pens cost $12.50, what is the cost of 8 pens?

$\text{Cost per pen} = \frac{\$12.50}{5 \text{ pens}}$ $\text{Cost per pen} = \$2.50 \text{ per pen}$

$\text{Cost of 8 pens} = \$2.50/\text{pen} \times 8 \text{ pens}$ $\text{Cost of 8 pens} = \$20.00$ The cost of 8 pens is \boxed{\text{\20}}$.

Q3) A train travels at 90 km/h. How far will it go in 2 hours and 30 minutes?

The train will go $\boxed{\text{225 km}}$.

Q4) A man spends 3/5 of his salary. If he earns $2,500 monthly, how much does he save?

If he spends $\frac{3}{5}$ of his salary, he saves the remaining fraction.

$\text{Amount saved} = \frac{2}{5} \times \$2,500$ $\text{Amount saved} = \frac{2 \times \$2,500}{5}$ $\text{Amount saved} = \frac{\$5,000}{5}$ $\text{Amount saved} = \$1,000$ He saves \boxed{\text{\1,000}}$.