Cogito
Grade 7 Math · Chapter 3 · Lesson 4
Simple Interest
What money earns for sitting still.
10 problems · about 18 minutes · 7.RP.A.3
What this lesson teaches
The child calculates simple interest and the total after a number of years.
- Simple interest is a fixed percent of the original, paid each year.
- Interest = amount × rate × years.
- Check whether the question wants the interest or the total.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Discounts and Sale Prices: £70 with 20% off. Pay in pounds?
Answer 56
Why £56.
Review — Tax, Tips, and Markup: £90 with 20% added. Total in pounds?
Answer 108
Why £108.
Review — Percent Increase and Decrease: A 120 pound item falls 25%. New price?
Answer 90
Why 90 pounds.
Warm Up
Straightforward practice. Get the method working first.
3 problems£600 at 5% for 2 years. Interest in pounds?
Answer 60
Why £60.
£1000 at 3% for 1 year. Interest in pounds?
Answer 30
Why 3% of 1000.
£1000 at 3% for 4 years. Interest in pounds?
Answer 120
Why £30 a year.
Build It Up
The same ideas with more to keep track of.
2 problems£200 at 10% for 3 years. Total in pounds?
Answer 260
Why £20 a year, then add on.
Does simple interest take the percent from the growing total? Answer 1 for yes, 0 for no.
Answer 0
Why Always from the original.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Savings: £400 at 5% for 2 years. How much interest, in pounds?
Answer 40
Why £40.
The Total: Same account. How much altogether, in pounds?
Answer 440
Why £440.