How much is 15% of 200 · Kode bersama Martin

Fifteen percent of two hundred — two paths, one result

Today the first big calculation with percentages: how much is 15% of 200? You will learn two paths. Both lead to the same number, each is handy somewhere else.

The path via 1%. First find how much one hundredth of the whole is: 200 : 100 = 2. One percent is 2. Fifteen percent is fifteen times that: 15 × 2 = 30.

The path via a decimal. Convert the percent to a decimal and multiply: 15% = 0.15, so 0.15 × 200 = 30.

The path via 1% is great in your head and on paper — you always know what you are counting. The path via a decimal is faster with a calculator. Pick one, but know both: in a test the first one helps, at the till the second.

And a third trick for lazy counters: 10% you find by shifting the point. From that you can build almost everything — 5% is half of a tenth, 20% two tenths, 15% is 10% + 5%.

Filip is saving for headphones at 1 200 Kč. Dad promised: “I will add 15% of the price.” Filip counts out loud at dinner: “One percent of 1 200 is 12. Fifteen percent is 15 × 12… 180.” Tereza checks the second path on her phone: 0.15 × 1200 = 180. That checks out. Dad smiles: “And how much do you still need to save?” Filip: “1 200 minus 180… 1 020.” — “See, percentages are not school bullying. It is 180 korunas extra.”

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Ten percent you find by shifting the decimal point one place left: 10% of 340 is 34. From tenths you build 5%, 15%, 20%, 30% — no calculator.

Two paths to a percent of a number

Path 1: via one percent.

Step 1: divide the base (the whole) by a hundred → you get 1%. Step 2: multiply by the number of percent.

How much is 24% of 350? One percent: 350 : 100 = 3.5. Then 24 × 3.5 = 84.

Path 2: via a decimal.

Step 1: convert the percent to a decimal (divide by a hundred): 24% = 0.24. Step 2: multiply the base: 0.24 × 350 = 84.

It is one and the same calculation, just in a different order. It always comes out the same.

Path 3 (for fast ones): building from anchors. 24% = 25% − 1%. A quarter of 350 is 87.5, one percent is 3.5, so 87.5 − 3.5 = 84. It works when the percent is close to a nice anchor.

Estimate before you calculate. Sebelum mulai, say roughly: 24% is almost a quarter, a quarter of 350 is a bit over 85. If you then get 840 or 8.4, you know a decimal point ran away. An estimate is a free safety net.

How much is 35% of 400?

Estimate: 35% is a bit over a third, a third of 400 is about 133. I expect a result around 140.

Path via 1%: one percent of 400 is 400 : 100 = 4. Then 35 × 4 = 140.

Path via a decimal: 35% = 0.35. I count 0.35 × 400 = 140.

Result: 140. Both paths the same, the estimate fits. If one path gave 140 and the other 14, I look for a lost decimal point.

How much is 6% of 1 500 Kč?

Watch single-digit percents — that is where a zero most often gets lost.

Path via 1%: 1 500 : 100 = 15. Six percent: 6 × 15 = 90.

Path via a decimal: 6% = 0.06 (not 0.6!). I count 0.06 × 1500 = 90.

Result: 90 Kč. Check: 10% of 1 500 is 150. Six percent must be smaller than 150 and bigger than half of that (75). The number 90 sits between them. Who writes 0.6 instead of 0.06 gets 900 — ten times too much.

Building from tenths: 15% of 640 with no calculator

Step 1: I find 10% by shifting the point: 10% of 640 is 64.

Step 2: 5% is half of that: 64 : 2 = 32.

Step 3: 15% = 10% + 5% = 64 + 32 = 96.

Result: 96. All in your head, no written multiplication. The same way you build 20% (2 × 64 = 128) or 30% (192). Use this trick in a shop when you want to know quickly how much you save.

⚠️

A lost zero with small percents. 6% is 0.06, not 0.6. Who hurries writes 0.6 and the result is ten times bigger. After calculating, always check the result with an estimate via 10%.

Play it

Before you go to the sheet, try it with your eyes. This is not a test — it is a game. Tap until you see it.

Practice: now you do it 🎲

Now try it for real. You will see all the questions at once, like on paper. Mulai with ten. When it goes well, add more.

Calculate a percent of a number. The bar at the top shows how many percent you take.

Practise the questions

On paper: both paths side by side

Calculate each question both ways and compare the results. They must match.

Calculate 45% of 300: first via 1% (300 : 100, then × 45), then via 0.45 × 300.
Calculate 8% of 2 500 Kč. Watch the writing 0.08 and check the result via 10%.
With no calculator, build from tenths: 30% of 240 and 15% of 180. Write the middle steps (10%, 5%).
There are 480 pupils in the school and 55% are girls. How many girls go to the school? First write an estimate, then calculate.

Now you 💪

I can find 1% by dividing the base by a hundred and from there any percent.
I can multiply by a decimal (15% = 0.15) and I do not mix 0.06 with 0.6.
Before calculating I make an estimate and after calculating I compare it with the result.

✅

Done when: All four questions have a result calculated two ways, both paths match and the estimates fit the results.

What to take from this lesson

Path 1: base : 100 = one percent, then times the number of percent.
Path 2: the percent as a decimal times the base.
Ten percent = a shift of the decimal point. Building from tenths you can count almost everything.
Small percents have an extra zero: 6% = 0.06.
An estimate before calculating catches a lost point.