Watch your savings grow. Find a percent of money, earn simple and compound interest, work out sale prices, solve missions and puzzles and beat the clock.
Start here. A bank keeps your savings safe and pays you a little extra for it. That extra money is called interest. The money you start with is the principal. The percent the bank pays each year is the interest rate. In this game the rates are easy numbers so you can work them out in your head. Real bank rates are usually smaller.
Percent of an amount. Percent means "out of 100". So 10% of $200 is 10 out of every 100 dollars, which is $20. Some percents are easy: 50% is half, 25% is a quarter and 10% is a tenth. For 20% find 10% and double it.
Simple interest. With simple interest you earn the same amount every year. Interest = savings × rate ÷ 100 × years. If you save $500 at 10%, you earn $50 each year, so $150 in 3 years.
Compound interest. With compound interest the interest is added to your savings every year, so next year you earn interest on the interest too. Save $1,000 at 10%: after year 1 you have $1,100, after year 2 $1,210 and after year 3 $1,331. Simple interest would give only $1,300. The extra $31 is interest on interest.
Prices that change. A price that goes up 20% becomes 120% of the old price. A price that is 20% off becomes 80% of the old price. Find the change first, then add it or take it away. When two changes happen, such as a discount and then tax, do them one after the other. Do not just add the percents.
Common mix-ups. The rate is per year, so check how many years there are. Compound interest is worked out year by year, not all at once. Tax is added to the sale price, not to the old price.
Try this above. In Play, change the savings, the rate and the years and watch the gold bars grow. At level 3 press Both to see how much extra compound interest earns. At level 2 open Prices to try sales.
Interest is money a bank pays you for keeping your savings with it. If you borrow money, you pay interest instead. The percent the bank pays each year is the interest rate.
With simple interest you earn the same amount every year. With compound interest the interest is added to your savings, so next year you earn interest on the interest too. Compound interest grows faster the longer you wait.
Percent means "out of 100". To find 10% divide by 10. To find 50% divide by 2. To find 25% divide by 4. For other percents, find 10% or 1% first and multiply.
Find the discount first: the percent of the old price. Then take it away from the old price. A $50 item at 20% off has a discount of $10, so the sale price is $40.
Just starting: percent of an amount and one year of interest. I know the basics: simple interest for several years and percent increase and decrease. Challenge me: compound interest, comparing accounts and two-step prices.
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