ISEE Lower Level

Percent Calculations

Calculating percentages, percent increase/decrease, and applied percent problems (tax, tip, discount, successive percent changes)

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Imagine you're playing your favorite video game, and you find a treasure chest that gives you a 50% health boost! Or maybe you're at the store buying a cool new skateboard, and there's a giant sign that says 20% OFF! Percents are everywhere in the real world, and they are definitely going to pop up on the ISEE! 🎮🛹

But what exactly is a percent? The word percent is actually a secret code. 'Per' means 'for every,' and 'cent' means 'one hundred' (just like there are 100 cents in a dollar or 100 years in a century). So, 50% just means 50 for every 100. If you have a giant pizza cut into 100 tiny slices (whoa, that's a lot of cutting!), 50% means you get 50 slices. 🍕

On the ISEE, you'll need to know how to find the percent of a number, figure out what percent one number is of another, and calculate percent changes (like when a price goes up or down). The secret trick is to remember that percents can always be turned into fractions or decimals to make the math way easier. For example, 25% is just $\frac{25}{100}$ , which simplifies to $\frac{1}{4}$ .

Let's learn some awesome shortcuts so you can crush these percent questions and feel 100% confident on test day! Remember, there is no penalty for guessing on the ISEE, so if a question looks tricky, use your best real-world logic and go for it!

Key Formula

To find a percent change, use this formula:

Percent Change = \frac{Amount of Change}{Original Amount} \times 100

Practice Questions

4 practice questions for ISEE Lower Level

Q1 Easy

What is

25%

80

10

20

30

40

Show Solution

To find $25%$ of $80$ , you can convert $25%$ to a decimal or a fraction.

As a decimal: $25% = 0.25$ .
Multiply $0.25$ by $80$ : $0.25 \times 80 = 20$ .
As a fraction: $25% = \frac{25}{100} = \frac{1}{4}$ .
Multiply $\frac{1}{4}$ by $80$ : $\frac{1}{4} \times 80 = \frac{80}{4} = 20$ .
So, $25%$ of $80$ is $20$ .

Answer: B

Q2 Easy

A toy car originally cost $

15

. If its price increased by

20%

, what is the new price of the toy car?

A $

12

B $

17

C $

18

D $

20

Show Solution

First, calculate the amount of the price increase.

Increase amount = $20%$ of $ $15$
Convert $20%$ to a decimal: $0.20$ .
Increase amount = $0.20 \times 15 = 3$ .
The price increased by $ $3$ .
Now, add the increase amount to the original price to find the new price:
New price = Original price + Increase amount
New price = $ $15 + 3 = 18$ .
The new price of the toy car is $ $18$ .

Answer: C

Q3 Easy

12

60%

of what number?

18

20

25

30

Show Solution

Let the unknown number be $x$ .

We can write the problem as an equation:
$12 = 60% \times x$
Convert $60%$ to a decimal: $0.60$ .
So, the equation becomes:
$12 = 0.60 \times x$
To find $x$ , divide $12$ by $0.60$ :
$x = \frac{12}{0.60}$
$x = 20$ .
So, $12$ is $60%$ of $20$ .

Answer: B

Q4 Easy

A book usually costs $

20

. During a sale, it is offered at a

10%

discount. How much money do you save if you buy the book during the sale?

A $

1

B $

2

C $

18

D $

19

Show Solution

The amount you save is the discount amount.

Discount amount = $10%$ of the original price.
Original price = $ $20$ .
Discount percentage = $10%$ .
Convert $10%$ to a decimal: $0.10$ .
Calculate the amount saved:
Amount saved = $0.10 \times 20 = 2$ .
You save $ $2$ if you buy the book during the sale.

Answer: B

Tips & Strategies

Memorize common percent-to-fraction conversions like $25% = \frac{1}{4}$ , $50% = \frac{1}{2}$ , and $75% = \frac{3}{4}$ . It saves tons of time on the math sections!
Use the '10% trick'. To find 10% of any number, just move the decimal point one spot to the left. For example, 10% of 450 is 45. Need 20%? Just double that 45 to get 90!
For Quantitative Comparison questions, remember the magic rule: $A % of B$ is always equal to $B % of A$ . If you see this on the ISEE, you can pick (C) without doing any math!

Common Mistakes

Watch out for percent change questions! A huge mistake is dividing the change by the NEW number instead of the ORIGINAL number. Always put the difference over the starting amount.
Don't forget that 'percent' means 'out of 100'. If an ISEE question asks for $5%$ of a number, make sure you multiply by $0.05$ or $\frac{5}{100}$ , not $0.5$ (which is actually $50%$ !).

Frequently Asked Questions

Do I have to use fractions, or can I use decimals?

You can use whichever one you like best! Sometimes decimals are easier, but fractions are usually faster on the ISEE if you simplify them first.

What if I forget a formula during the test?

Don't panic! Remember that 'percent' just means 'cents in a dollar'. If you need 25% of 80, just think 'what is a quarter of 80?' Use your real-world logic!

Is there a penalty for guessing on the ISEE if I can't figure out the percent?

Nope! There is zero penalty for guessing on the ISEE. If a percent question has you totally stumped, eliminate any crazy answers, take your best guess from the remaining choices, and move on.

How can I quickly find 15% of a number?

Find 10% first by moving the decimal to the left once. Then cut that number in half to find 5%. Add those two numbers together and you have 15%!

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