Estimate sums

key notes:

Understanding Estimation

  • Estimation means finding a number close to the exact sum.
  • It helps in quick calculations and checking answers.

Rounding Numbers

  • Round numbers to the nearest 10 to make adding easier.
  • Example: 47 rounds to 50, 32 rounds to 30.

Using Benchmark Numbers

  • Identify numbers close to 10, 20, 50, or 100 to estimate sums quickly.

Mental Math Strategies

  • Use friendly numbers (like 10, 20, 50) to estimate sums.
  • Example: Estimate 48 + 23 → round to 50 + 20 = 70.

Estimating with Two-Digit Numbers

Look at the tens place to decide how to round.

Example: 56 + 38

  • Round to 60 + 40 = 100 (estimated sum).

Checking Reasonableness

  • Compare estimated sum with actual sum to see if it makes sense.

Importance of Estimation

  • Helps in real-life situations like shopping, time management, and planning.

Learn with an example

✈️ Estimate the sum by rounding each number to the nearest ten and then adding. 51 + 31

The sum is approximately ___________.

  • Round each number to the nearest ten.
  • Now add: 50 + 30 = 80
  • The sum is about 80.

✈️ Which addition problem has a sum of about 70?

  • 11 + 41
  • 28 + 41
  • 11 + 13
  • 62 + 19
  • Estimate each sum by rounding each number to the nearest ten, then adding.
  • This problem has a sum of about 50.
  • This problem has a sum of about 70.
  • This problem has a sum of about 20.
  • This problem has a sum of about 80.

✈️ Estimate the sum by rounding each number to the nearest ten and then adding.

43 + 37

The sum is approximately ________.

  • Round each number to the nearest ten.
  • Now add: 40 + 40 = 80
  • The sum is about 80.

Let’s practice!🖊️