MathGrade 10ages 15–16
🌱 Percent growth
Growing by 10% every year for two years adds up to more than 20% overall, because each year's growth multiplies onto the year before's new, bigger total — not onto the original amount.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- Adding ten percent is multiplying by one and a tenth.
- In repeated growth you multiply again and again, because each year starts from the new total.
- That is why two years of ten percent give more than twenty percent.
- Taking ten percent off is multiplying by nine tenths.
The mistake most kids make here
Multiplying the percent by the number of years instead of repeating the growth.
Try one question
To add 10 percent, what do you multiply by?
Adding 10 percent
- by one and a tenth
- by a tenth
- by ten
Answer
by one and a tenth — That's it. The one keeps what there was, and the tenth adds to it.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: Say what you multiply by to add ten percent.
How to help at home
Adding 10% to any amount is the same as multiplying that amount by 1.1. The key idea in repeated growth is that each year, you multiply by 1.1 again — starting from last year's total, not from the very first amount.
Try it with real numbers: start with 100 shekels. After one year of 10% growth, it's 110. After a second year of 10% growth on the new total, it's 110 × 1.1 = 121 — not 120, which is what 20% of the original 100 would give.
When your child multiplies the percent by the number of years (assuming two years of 10% is just 20%), walk through the two separate steps above with them, one year at a time, and let them see the gap between 121 and 120 for themselves.
A sign they've got it: they can explain, in their own words, why compounding twice at 10% beats a single jump of 20%, because the second 10% is taken from a bigger number than the first.
Questions parents ask
- Why doesn't 10% growth for two years equal 20% growth?
- Because the second year's 10% is calculated on the new, already-grown total from year one — not on the original amount — so it adds a bit more than a flat 20% would.
- How do I calculate a 10% increase quickly?
- Multiply the amount by 1.1. The 1 keeps the original amount, and the 0.1 adds ten percent of it on top, in a single multiplication.
- What about decreasing by a percentage repeatedly?
- The same idea applies with a smaller multiplier: decreasing by 10% each time means multiplying by 0.9 repeatedly, with each year's drop calculated on the smaller new total.
- How does Maya teach repeated percent growth?
- Maya has the child compute one year of growth at a time and use that year's result as the starting point for the next, so the compounding effect is seen step by step rather than assumed away.
No card needed. The first lesson is free.
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