What is 15 + 15?

S1-SA1-1207

Grade Level:

Class 2

Maths, Computing, AI

Definition

What is it?

15 + 15 means adding the number 15 to itself. It is a basic addition problem where we combine two groups of 15 items to find the total.

Simple Example

Quick Example

Imagine you have two friends. Each friend gives you 15 colourful marbles. To find out how many marbles you have in total, you would add 15 (from the first friend) and 15 (from the second friend).

Worked Example

Step-by-Step

Let's find the sum of 15 + 15:

1. Write the numbers one below the other, aligning the ones place and tens place:
15
+ 15
-----

2. First, add the digits in the ones place: 5 + 5 = 10.

3. Write '0' in the ones place of the answer and carry over '1' to the tens place.
¹
15
+ 15
-----
0

4. Next, add the digits in the tens place, including the carried-over '1': 1 + 1 + 1 (carried over) = 3.

5. Write '3' in the tens place of the answer.
¹
15
+ 15
-----
30

So, 15 + 15 = 30.

Why It Matters

Understanding addition like 15 + 15 is fundamental for Maths, Computing, and even AI. It's the building block for more complex calculations used by computer programmers to create apps or by data scientists to analyze large datasets. Even game developers use such basic arithmetic for scoring and character movements.

Common Mistakes

MISTAKE: Adding only the tens place or only the ones place. For example, getting 10 (5+5) or 2 (1+1) as the answer. | CORRECTION: Always add both the ones place and the tens place (and any other places) separately, remembering to carry over when needed.

MISTAKE: Forgetting to carry over the '1' when the sum of the ones place is 10 or more. For example, writing 210 instead of 30. | CORRECTION: When 5 + 5 gives 10, write '0' in the ones place and carry the '1' to the tens place column to be added there.

MISTAKE: Confusing addition with multiplication. Thinking 15 + 15 is the same as 15 x 15. | CORRECTION: Addition means combining numbers, while multiplication is repeated addition. 15 + 15 is two groups of 15, while 15 x 15 means 15 groups of 15.

Practice Questions

Try It Yourself

QUESTION: If you have 15 ladoos and your friend gives you another 15 ladoos, how many ladoos do you have in total? | ANSWER: 30 ladoos

QUESTION: What is the sum of 12 + 12 + 6? (Hint: First add 12 + 12, then add 6 to that answer) | ANSWER: 30

QUESTION: Riya had 15 rupees. Her mother gave her 15 rupees more. She then bought a pen for 5 rupees. How much money does Riya have left? | ANSWER: 25 rupees

MCQ

Quick Quiz

Which of these sums equals 30?

10 + 10

15 + 15

20 + 5

25 + 10

The Correct Answer Is:

15 + 15 correctly adds up to 30. Option A (10+10=20), Option C (20+5=25), and Option D (25+10=35) are incorrect sums.

Real World Connection

In the Real World

When you're shopping at a local kirana store and buy two items that each cost 15 rupees, you quickly calculate 15 + 15 = 30 rupees to know the total bill. This basic addition is used every day by shopkeepers, bus conductors, and even when you track your cricket scores!

Key Vocabulary

Key Terms

ADDITION: Combining two or more numbers to find their total sum | SUM: The result of adding two or more numbers | ONES PLACE: The rightmost digit in a number, representing single units | TENS PLACE: The digit to the left of the ones place, representing groups of ten | CARRY OVER: Moving a digit (usually a '1') from one column to the next column on the left during addition.

What's Next

What to Learn Next

Now that you've mastered adding two-digit numbers like 15 + 15, you're ready to learn about adding three-digit numbers or even subtraction. These concepts build on the same ideas of place value and carrying over, making you a maths superstar!