1. First estimate and then do the for a) \( (453942+275931)-317908 \) b) \( (1580342+1385211)-488011 \) c) \( 30689755-(10221007+199676) \) d) \( 902879355-(302345757+122288533) \) 2. Work out the answers to the following calculations: a) \( (154899+176807)-(109344+89003) \) b) \( (340376933-280175698)+(301438544-110237843) \) c) \( (7543128-3241352)-(2123473-0) \)

Below are the step‐by‐step workings for both the estimation (with final exact answers) and the precise calculations. ────────────────────────────── 1. Estimation and then exact calculation a) (453942 + 275931) – 317908  • Estimate:   – 453942 ≈ 454000   – 275931 ≈ 276000   – Sum ≈ 454000 + 276000 = 730000   – 317908 ≈ 318000   – Estimated answer ≈ 730000 – 318000 = 412000  • Exact Calculation:   1. Sum inside the bracket: 453942 + 275931 = 729873   2. Then subtract: 729873 – 317908 = 411965 b) (1580342 + 1385211) – 488011  • Estimate:   – 1580342 ≈ 1580000   – 1385211 ≈ 1385000   – Sum ≈ 1580000 + 1385000 = 2965000   – 488011 ≈ 488000   – Estimated answer ≈ 2965000 – 488000 = 2477000  • Exact Calculation:   1. Sum: 1580342 + 1385211 = 2965553   2. Subtract: 2965553 – 488011 = 2477542 c) 30689755 – (10221007 + 199676)  • Estimate:   – 10221007 ≈ 10221000   – 199676 ≈ 200000   – Sum inside parentheses ≈ 10221000 + 200000 = 10421000   – 30689755 – 10421000 ≈ 20268755 (about 20269000)  • Exact Calculation:   1. First compute: 10221007 + 199676 = 10420683   2. Then subtract: 30689755 – 10420683 = 20269072 d) 902879355 – (302345757 + 122288533)  • Estimate:   – 302345757 ≈ 302350000   – 122288533 ≈ 122290000   – Sum ≈ 302350000 + 122290000 = 424640000   – 902879355 – 424640000 ≈ 478239355 (about 478245000)  • Exact Calculation:   1. Sum: 302345757 + 122288533 = 424634290   2. Then subtract: 902879355 – 424634290 = 478245065 ────────────────────────────── 2. Precise Calculations a) (154899 + 176807) – (109344 + 89003)  1. First calculate the sums in the parentheses:   – 154899 + 176807 = 331706   – 109344 + 89003 = 198347  2. Then subtract:   331706 – 198347 = 133359 b) (340376933 – 280175698) + (301438544 – 110237843)  1. Compute each difference separately:   – 340376933 – 280175698 = 60201235   – 301438544 – 110237843 = 191200701  2. Then add the results:   60201235 + 191200701 = 251401936 c) (7543128 – 3241352) – (2123473 – 0)  1. First difference:   – 7543128 – 3241352 = 4301776  2. Then subtract the second term:   – (2123473 – 0) = 2123473   – So, 4301776 – 2123473 = 2178303 ────────────────────────────── Final Answers: 1. Estimation and Exact Results:  a) 411965     b) 2477542  c) 20269072    d) 478245065 2. Precise Calculations:  a) 133359     b) 251401936    c) 2178303 These are the complete solutions for the given problems.