Mentally Find 1,000, 10,000, or 100,000 More or Less
This Grade 4 Eureka Math skill teaches students to mentally add or subtract 1,000, 10,000, or 100,000 from a multi-digit number by changing only the digit in the corresponding place value. To find 10,000 more than 145,280, students increase the ten-thousands digit from 4 to 5, giving 155,280. To find 1,000 less than 38,612, they decrease the thousands digit from 8 to 7, giving 37,612. Covered in Chapter 2 of Eureka Math Grade 4, this mental math skill builds place value fluency with six-digit numbers.
Key Concepts
To find a number that is $1,000$, $10,000$, or $100,000$ more or less than a given number, identify the digit in the corresponding place value (thousands, ten thousands, or hundred thousands). Increase the digit by 1 to find the number that is more, or decrease it by 1 to find the number that is less.
Common Questions
How do you mentally find 10,000 more than a number?
Identify the ten-thousands digit and increase it by 1. For 145,280, the ten-thousands digit is 4; adding 1 gives 155,280. All other digits stay the same.
How do you mentally find 1,000 less than 38,612?
Find the thousands digit (8) and decrease it by 1 to get 7. The result is 37,612.
How do you find 100,000 less than 759,000?
Decrease the hundred-thousands digit by 1: 7 becomes 6, giving 659,000.
Why can you change just one digit when adding or subtracting these amounts?
Because 1,000, 10,000, and 100,000 each affect only one specific place value. As long as no regrouping is needed, all other digits remain unchanged.
What is the mental math strategy for adding 1,000 to 38,612?
Find the thousands digit (8) and add 1 to get 9. The result is 39,612. Only the thousands place changes.