The unknown here is the number of days it will take to save over 1000 pennies. Instead of an equation this is an inequality. The phrase "more than 1000 pennies" is > 1000. Now we need to figure out WHAT is more than 1000. If Jack starts with 2 pennies today, that is our "fixed" number. To that starting number of pennies we are doubling the number of pennies per day. Doubling means we are multiplying by 2. The mathematical expression for "doubling the number of pennies per day" is 2x. Adding in our starting amount of 2 pennies, we have
2x + 2 > 1000 and
2x > 998 so
x > 499
This means that it will take more than 499 days to get more than 1000 pennies. It will take 500 days to get exactly 1000, but that is not what we are asked to find.
