Number Essay

1003 WordsMay 26, 20145 Pages
Chapter 1 Whole numbers 43 remember remember 1. An estimation can be used when the exact answer is not required. 2. An estimation can be used to check a calculation. 3. A useful estimation can be made by rounding each number to the first digit and then performing the appropriate calculation. 4. If the second digit is 0, 1, 2, 3 or 4, the first digit stays the same. If the second digit is 5, 6, 7, 8 or 9, the first digit is increased by 1 or rounded up. 1G WORKED Estimation Math cad Example 1 Estimate 67 451 × 432. Estimation 14 2 Copy and complete the following table by rounding the numbers to the first digit. The first row has been completed as an example. In the column headed ‘Prediction’, guess whether the actual answer will be higher or lower than your estimate. Then use a calculator to work out the actual answer and record it in the final column titled ‘Calculation’ to determine whether it was higher or lower than your estimate. Is the actual answer higher or lower than the estimate? Estimate Estimated answer Prediction Calculation The four operations E L Spread XCE sheet 1.8 Rounding SkillS T HEE Example 4129 ÷ 246 4000 ÷ 200 20 Lower to the 16.784 553 first so lower (leading) digit a b c d e f 487 + 962 33 041 + 82 629 184 029 + 723 419 93 261 − 37 381 321 − 194 468 011 − 171 962 (continued) 44 Maths Quest for Queensland Book 1 Is the actual answer higher or lower than the estimate? Estimate Estimated answer Prediction Calculation g h i j k l 87 × 432 623 × 12 671 29 486 × 39 31 690 ÷ 963 63 003 ÷ 2590 37 009 ÷ 180 3 multiple choice a The best estimate of 4372 + 2587 is: A 1000 B 5527 b The best estimate of 672 × 54 is: A 30 000 B 35 000 c The best estimate of 67 843 ÷ 365 is: A 150 B 175 C 6000 C 36 000 C 200 D 7000 D 42 000 D 250 4 Estimate the answers to each of these. a

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