Example 1

Estimate to find whether each calculation is correct.

1. Calculation   Estimate $ 126.91 ≈ $ 130 $ 14.05 ≈ $ 10 + $ 25.14 ¯ ≈ + $ 30 ¯ $ 266.10   $ 170 table with 5 rows and 3 columns , row1 column 1 , cap calculation , column 2 , column 3 cap estimate , row2 column 1 , dollars , 126.91 , column 2 almost equal to , column 3 dollars 130 , row3 column 1 , dollars , 14.05 , column 2 almost equal to , column 3 dollars 10 , row4 column 1 , modified plus dollars , 25.14 with under bar below , column 2 almost equal to , column 3 modified plus dollars 30 with under bar below , row5 column 1 , dollars , 266.10 , column 2 , column 3 dollars 170 , end table

   The answer is not close to the estimate. It is not reasonable. The calculation is incorrect.

2. Calculation   Estimate 372.85 ≈ 370 − 227.31 ¯ ≈ − 230 ¯ 145.54   140 table with 4 rows and 3 columns , row1 column 1 , cap calculation , column 2 , column 3 cap estimate , row2 column 1 , 372.85 , column 2 almost equal to , column 3 370 , row3 column 1 , modified negative , 227.31 with under bar below , column 2 almost equal to , column 3 modified negative 230 with under bar below , row4 column 1 , 145.54 , column 2 , column 3 140 , end table

   The answer is close to the estimate. It is reasonable. The calculation is correct.

Example 2

Tomatoes cost $3.54, squash costs $2.75, and lemons cost $1.20. Estimate the total cost of the produce.

Add the 3.54 → 0.50 Estimate by rounding .  Then add . front-end digits . 2.75 → 0.80     + 1.20 ¯ → + 0.20 ¯     6   1.50   table with 4 rows and 5 columns , row1 column 1 , cap addthe , column 2 3.54 , column 3 rightwards arrow , column 4 0.50 , column 5 cap estimatebyrounding . . . cap thenadd . . , row2 column 1 , frontminusenddigits . . , column 2 2.75 , column 3 rightwards arrow , column 4 0.80 , column 5 , row3 column 1 , , column 2 modified plus , 1.20 with under bar below , column 3 rightwards arrow , column 4 modified plus , 0.20 with under bar below , column 5 , row4 column 1 , , column 2 6 , column 3 , column 4 1.50 , column 5 , end table

Since 6 + 1.50 = 7.50 , 6 plus , 1.50 , equals , 7.50 , comma  the total cost is about $7.50.