Mental Maths Subtraction Strategies

Study Notes

Mental Maths Subtraction Strategies

Compatible Numbers Approach

Uses numbers that are easy to compute.
Adjusts one or both numbers to nearby values that make subtraction simpler.
Example: For 52 - 27, adjust 27 to 30, calculate 52 - 30 = 22, then add 3 back: 22 + 3 = 25.

Counting Back Strategy

Subtracts by counting backwards from the minuend.
Start with the larger number and count down to the smaller number.
Useful with smaller numbers or when exact values are known.
Example: To calculate 15 - 7, count back from 15: 14, 13, 12, 11, 10, 9, 8 = 8 (15-7=8).

Bridging Ten Technique

Focuses on reaching a 'ten' to simplify calculations.
Breaks down numbers to make subtracting easier.
Example: For 23 - 9, think: 23 - 3 (to make 20) = 20, then subtract the remaining 6 from 20: 20 - 6 = 14.

Number Line Strategy

Visualizes subtraction on a number line.
Jumps backward from the starting number (minuend) to reach the endpoint (subtrahend).
Can be used for both small and larger numbers, enhancing understanding of distance between values.

Partitioning Method

Breaks numbers into smaller, more manageable parts.
Subtracts each part separately and then combines results.
Example: For 63 - 25, partition as (60 - 20) and (3 - 5). Calculate: 60 - 20 = 40; for 3 - 5, recognize it can't be done, borrow from 40 making it 39, leading to a final answer of 38.

Compatible Numbers Approach

Makes subtraction problems easier by adjusting numbers to nearby values that are simpler to work with.
Example: Instead of 52 - 27, adjust 27 to 30: 52 - 30 = 22. Then add 3 back to compensate: 22 + 3 = 25.

Counting Back Strategy

Involves mentally subtracting by counting backwards from the larger number (minuend) to reach the smaller number.
Useful with smaller numbers or when precise values are known.
Example: To find 15 - 7, count backwards from 15: 14, 13, 12, 11, 10, 9, 8. The last number in the count (8) is the answer.

Bridging Ten Technique

Focuses on reaching a 'ten' to simplify subtraction.
Breaks numbers down to make the calculation easier.
Example: For 23 - 9, think: 23 - 3 = 20 (to reach a ten). Then subtract the remaining 6: 20 - 6 = 14.

Number Line Strategy

Uses a visual representation (number line) to visualize subtraction.
You jump backwards from the starting number (minuend) to reach the endpoint (subtrahend).
Helpful for understanding the distance between values for both small and larger numbers.

Partitioning Method

Divides numbers into smaller, more manageable parts.
Subtracts each part separately and then combines the results.
Example: To solve 63 - 25, break it down to (60 - 20) and (3 - 5). Calculate: 60 - 20 = 40. For 3 - 5, borrow 1 from the '40' to create 39, resulting in a final answer of 38.

Decomposing Numbers

To subtract two-digit numbers, decompose them into smaller units, making the calculation easier.
Subtract the smaller parts individually before summing the results.
For example, 58 - 27 becomes (58 - 20) - 7 which simplifies to 38 - 7 = 31.

Using Complements

Instead of directly subtracting, find the difference to the next ten.
This works well with single-digit subtractions.
For example, 43 - 9 can be thought of as 43 - (10 - 1).
Subtract 10 from 43 (33), then add 1 back to get 34.

Bridging Through Ten

Adjust the subtrahend to reach a ten, making subtraction simpler.
This is effective for numbers near a ten.
For example, 52 - 9 can be transformed into (52 - 10 ) + 1.
Subtract 10, giving 42, then add back 1 for the final answer of 43.

Rounding And Adjusting

Simplify the calculation by rounding the subtrahend to the nearest ten and then adjusting for the difference.
Example: For 76 - 29, round 29 to 30.
Subtract 30 from 76, giving 46. Then add back the 1 due to rounding to reach 47.

Number Line Strategy

Visualize the subtraction problem on a number line.
Start at the minuend and move left (backward) along the number line by the value of the subtrahend.
For example, to find 86 - 23, move left 20 (to 66) and then 3 (to 63).
This method visually demonstrates the concept of subtraction.

Description

Explore various strategies for mental subtraction to enhance your mathematical skills. This quiz covers techniques like compatible numbers, counting back, bridging ten, and using a number line. Each method simplifies subtraction for easier calculations and better understanding.