Compare and Order Whole Numbers and Decimals

SECTION 1

Why Do We Compare Numbers?

People have been comparing numbers for thousands of years! Imagine a farmer long ago with two baskets of apples. She needed to know which basket had more. That's comparing numbers!

Over time, people invented clever ways to write and compare amounts. Let's look at some big moments in the history of numbers.

3000 BC

Ancient Egyptians Count

The Egyptians used symbols to write numbers. They compared amounts to trade and build pyramids.

500 AD

Decimals Are Born in India

Mathematicians in India created the decimal system we use today, with digits 0 through 9 and place value.

1600s

The Symbols > and < Appear

Thomas Harriot invented the greater-than (>) and less-than (<) symbols. These made comparing numbers much easier to write!

Today

Comparing Numbers Everywhere

We compare numbers every day — prices at the store, scores in games, and temperatures on the weather report.

On the ISEE, you will compare and put numbers in order. This includes whole numbers like 345 and decimals like 3.45. Let's learn exactly how to do it!

SECTION 2

Core Principles of Comparing Numbers

Before we compare numbers, we need to understand a few important ideas. These are the building blocks that make everything easier!

Place Value

Each digit in a number has a value based on its position. The digit 5 in 500 is worth way more than the 5 in 50.

Compare from Left to Right

Always start comparing digits on the left side. The leftmost digit has the biggest value. If those digits match, move one spot to the right.

Symbols: > < =

Use > for greater than, < for less than, and = for equal. The open side of the symbol always faces the bigger number!

Line Up Decimal Points

When comparing decimals, always line up the decimal points first. You can add zeros at the end to make numbers the same length. For example, 3.5 is the same as 3.50.

Ordering Means Sorting

Ordering numbers means putting them in a line from least to greatest (smallest first) or greatest to least (biggest first).

✦ KEY TAKEAWAY

Think of comparing numbers like comparing two buildings. First, check which one has more floors (more digits). If they have the same number of floors, start at the top floor and compare one floor at a time going down. The building with a bigger number on any floor first — wins!

SECTION 3

Seeing Numbers on a Number Line

A number line is one of the best tools for comparing numbers. Numbers to the right are always bigger. Numbers to the left are always smaller.

On a number line, numbers to the right are always greater. The violet dot (25) is to the left of the pink dot (45), so 25 < 45. The same rule works for decimals: 3.15 is to the left of 3.65, so 3.15 < 3.65.

The number line makes it easy to see! When you're not sure which number is bigger, picture where each number sits on the line. The one farther to the right is the bigger number.

SECTION 4

The Step-by-Step Method

Here is the exact method you can use every time you compare numbers on the ISEE. Follow these steps and you'll get it right!

Comparing Whole Numbers

STEP 1: COUNT THE DIGITS

More digits = Bigger number

A 4-digit number is always greater than a 3-digit number. For example, 1,000 > 999.

STEP 2: SAME NUMBER OF DIGITS? COMPARE LEFT TO RIGHT

Start at the leftmost digit and compare

If both numbers have the same number of digits, look at the leftmost digit first. The number with the bigger leftmost digit is greater. If they match, move to the next digit to the right.

Comparing Decimals

STEP 1: COMPARE THE WHOLE-NUMBER PART FIRST

Look at the number BEFORE the decimal point

For example, in 5.3 vs. 4.9, compare 5 and 4 first. Since 5 > 4, we know 5.3 > 4.9.

STEP 2: SAME WHOLE NUMBER? ADD ZEROS AND COMPARE

3.5 = 3.50 then compare 3.50 and 3.47

If the whole-number parts are the same, add zeros so both decimals have the same number of digits after the decimal point. Then compare digit by digit from left to right.

💡 ISEE Test Tip

On the ISEE, answer choices for number problems are listed in order from least to greatest (or greatest to least). This can help you check your work! If your answer doesn't fit the order, double-check your comparing.

SECTION 5

Place Value — The Secret to Comparing

Understanding place value is the secret weapon for comparing numbers. Each spot in a number is worth 10 times more than the spot to its right. Let's look at a place value chart!

This chart shows two numbers lined up by place value. We compare from left to right. The ten-thousands digits (4 = 4) match, and the thousands digits (2 = 2) match. At the hundreds place, 7 < 9, so Number A is less than Number B. We don't even need to look at the rest!

✦ KEY TAKEAWAY

Think of place value like a race. The leftmost digit is the fastest runner — it matters the most! If one number has a bigger "fastest runner," that number wins. You only check the slower runners if the fastest runners tie.

SECTION 6

Worked Example: Ordering Decimals

Let's put these numbers in order from least to greatest: 4.5, 4.08, 4.51, 4.1. Follow along step by step!

Order from Least to Greatest: 4.5, 4.08, 4.51, 4.1

Step 1 — Check the Whole-Number PartAll four numbers have the same whole-number part: 4. So we need to compare the decimal parts.

Step 2 — Add Zeros to Make Them the Same LengthMake every decimal have two digits after the decimal point by adding zeros at the end. This does NOT change their value!

4.50, 4.08, 4.51, 4.10

Step 3 — Compare the Tenths DigitLook at the tenths place (the first digit after the decimal). We have: 5, 0, 5, 1. The smallest tenths digit is 0 (in 4.08). The next smallest is 1 (in 4.10). Two numbers have 5 (4.50 and 4.51), so we need to compare those further.

So far: 4.08, 4.10, then 4.5_ and 4.5_

Step 4 — Compare the Hundredths for the Tied NumbersFor 4.50 and 4.51, look at the hundredths digit. We have 0 and 1. Since 0 < 1, 4.50 < 4.51.

4.50 comes before 4.51

Step 5 — Write the Final OrderPut them all together from least to greatest:

4.08, 4.1, 4.5, 4.51

📌 Remember!

Adding zeros after the last decimal digit does NOT change a number's value. 4.5 = 4.50 = 4.500. Use this trick every time to make comparing easier!

SECTION 7

Common Mistakes and How to Avoid Them

Even smart students make mistakes when comparing numbers. Let's look at the most common traps so you can avoid them on test day!

Watch out for these traps on the ISEE!

Common Mistake	Why It's Wrong	What To Do Instead
Thinking 4.12 > 4.9 because 12 > 9	You can't ignore the decimal point! Compare the tenths digit first: 1 < 9.	Add a zero: 4.12 vs. 4.90. Now compare: 1 < 9, so 4.12 < 4.9.
Thinking more digits after the decimal = bigger number	0.365 is NOT bigger than 0.9. The length doesn't matter — the digits do!	Always compare digit by digit from left to right after lining up the decimals.
Mixing up > and < symbols	It's easy to put the symbol the wrong way.	The open (big) end always faces the bigger number. Think of it like an alligator mouth that eats the bigger number!
Forgetting to compare all numbers when ordering	Skipping a number can put things in the wrong order.	Cross off each number as you place it in order. Make sure your final list has the same count.

🎯 ISEE STRATEGY

The biggest trap is comparing decimal digits as if they're whole numbers. Always line up the decimal points and add zeros first. If 4.9 becomes 4.90, you can clearly see that 90 hundredths is more than 12 hundredths!

SECTION 8

Connecting to Bigger Ideas

Comparing and ordering numbers is a skill you'll use in many areas of math. Let's see how this topic connects to other things you might see on the ISEE.

What You're Learning Now	Where It Leads Next
Comparing whole numbers	Rounding to the nearest ten, hundred, or thousand
Comparing decimals	Comparing fractions (like ½ vs. ¾) and money amounts ($3.49 vs. $3.52)
Ordering numbers from least to greatest	Reading data from tables and graphs, finding the smallest or largest value
Using place value to compare	Understanding how adding or subtracting changes a number's size

Every time you compare prices at a store, check the score of a game, or read a thermometer, you're using the same skills. You've got this!

🔬 Fun Fact

Scientists compare numbers with many decimal places when measuring things like the speed of light (299,792.458 kilometers per second) or the size of bacteria (0.001 millimeters). The same rules you're learning work for tiny and huge numbers!

SECTION 9

Practice Problems

Time to practice! Try each problem on your own first. Remember: on the ISEE, there's no penalty for wrong answers, so always pick an answer even if you're not 100% sure. Use process of elimination to cross out choices that can't be right.

Which symbol correctly completes the statement? 3,456 ___ 3,465

Which of the following is true?

Which list shows the numbers in order from least to greatest? 2.7, 2.09, 2.71, 2.07

Four students measured the length of a caterpillar. Their measurements in centimeters were: Maya: 5.6, Ben: 5.08, Lily: 5.62, Tom: 5.2. Which student's measurement was the greatest?

A number is greater than 6.45 but less than 6.5. Which of the following could be that number?

SUMMARY

Lesson Summary

To compare numbers, start by checking the number of digits — a number with more digits is usually greater. If two numbers have the same number of digits, compare them from left to right using place value. Stop as soon as you find a digit that's different. Use the symbols > (greater than), < (less than), and = (equal) to show your answer.

For decimals, the most important trick is to line up the decimal points and add zeros so all numbers have the same number of decimal places. Then compare digit by digit, just like with whole numbers. Remember, on the ISEE, always answer every question — there's no penalty for guessing. Use process of elimination to cross out choices that don't make sense. You've got this!