Subtracting a One-Digit Number from a Two-Digit Number

Key Concepts

1. Understanding Place Value

A two-digit number has a tens place and a ones place. For example, in the number 45, the digit 4 is in the tens place and represents 40, while the digit 5 is in the ones place and represents 5.

2. Subtracting a One-Digit Number

When subtracting a one-digit number from a two-digit number, you focus on the ones place. If the one-digit number is less than or equal to the digit in the ones place, you can subtract directly. If it is greater, you may need to "borrow" from the tens place.

Detailed Explanation

Direct Subtraction

If the one-digit number is less than or equal to the digit in the ones place, simply subtract it from the ones place. For example, to subtract 3 from 45:

45 - 3 = 42

Here, 5 (ones place) - 3 = 2, so the result is 42.

Borrowing from the Tens Place

If the one-digit number is greater than the digit in the ones place, you need to borrow from the tens place. For example, to subtract 8 from 45:

45 - 8 = 37

Here, 5 (ones place) is less than 8, so you borrow 1 from the tens place (4 becomes 3), making the ones place 15. Then, 15 - 8 = 7, and the tens place remains 3, so the result is 37.

Examples

Analogies

Analogy 1: Taking Away Toys

Imagine you have 35 toys and you give away 7 toys. You start with 5 toys in your hand and 3 groups of 10 toys. Since you can't give away 7 toys from just 5, you take one group of 10 (leaving 2 groups of 10) and add it to your 5 toys, making 15 toys. Now you can give away 7 toys, leaving you with 8 toys in your hand and 2 groups of 10 toys, which is 28 toys in total.

Analogy 2: Climbing Down Steps

Think of a two-digit number as a building with 10-step floors. If you are on the 45th step (4th floor and 5 steps down) and you need to climb down 8 steps, you first climb down the 5 steps on your floor, then move to the 3rd floor and climb down the remaining 3 steps, landing on the 37th step.