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Estimating Sums Using Ballpark Estimates and Partial Sums

This guide explains how to perform ballpark estimates and use partial sums in addition. By simplifying numbers to their nearest hundreds, we can quickly assess approximate totals. For example, when estimating 243 + 208, round each number to 200 for a quick ballpark estimate of 400. The same method applies to larger sums like 638 + 429, where rounding to 600 and 400 gives an estimated total of 1,000. The guide emphasizes the importance of checking if final answers are close to these estimates.

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Estimating Sums Using Ballpark Estimates and Partial Sums

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  1. Adding Partial Sums

  2. First you need to do a Ballpark Estimate 243 + 208 Ballpark Estimate:___________________________________

  3. Remember it’s easier to work with estimating when you only have 0s after the first number. 243  estimated to 200 + 208  estimated to 200 243 is closer to 200 than is it to 300. Ballpark Estimate:__200+200=400_________________________

  4. Remember how we expand numbers 243= 200 + 40 + 3 + 208= 200 + 0 + 8 Hundreds Tens Ones Ballpark Estimate:__200+200=400_________________________

  5. Remember how we expand numbers 243= 200 + 208= 200 Hundreds Tens Ones Ballpark Estimate:__200+200=400_________________________

  6. Remember how we expand numbers 243= 200 + 40 + 208= 200 + 0 Hundreds Tens Ones Ballpark Estimate:__200+200=400_________________________

  7. Remember how we expand numbers 243= 200 + 40 + 3 + 208= 200 + 0 + 8 Hundreds Tens Ones Ballpark Estimate:__200+200=400_________________________

  8. Hundreds Tens Ones 243 + 208 + 3 + 40 = 200 + 8 = 200 400 Think: 200 + 200 = 400 40 Think: 40 + 0 = 40 11 Think: 3 + 8 = 11 Does my answer make sense? Is it close to my ballpark estimate? 451 YES! Ballpark Estimate:__200+200=400_________________________

  9. First, make a Ballpark estimate. Let’s do another one 638 + 429 Ballpark Estimate:___________________________________

  10. Remember it’s easier to work with estimating when you only have 0s after the first number. 638  estimated to 600 + 429  estimated to 400 Ballpark Estimate:__600+400=1,000____________

  11. Keep in mind how we expand numbers so we can do partial sums 638= 600 + 30 + 8 + 429= 400 + 20 + 9 Hundreds Tens Ones Ballpark Estimate:__600+400=1,000_________________________

  12. Hundreds Tens Ones 638 + 429 + 8 + 30 = 600 + 20 + 9 = 400 1,000 Think: 600 + 400 = 1,000 50 Think: 30 + 20 = 50 17 Think: 8 + 9 = 17 Does my answer make sense? Is it close to my ballpark estimate? 1,067 YES! Ballpark Estimate:__600+400=1,000_________________________

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