Simplification and Approximation

(36 * 10^5) / (6 * 10^3) = (36/6) * 10^(5-3) = 6 * 10^2.

To express 0.000000125 in standard form, move the decimal point 7 places to the right to get 1.25. This corresponds to 1.25 * 10^-7.

Approximating the values: 15^2 - 7^2 + 5^2 = 225 - 49 + 25 = 201. The closest option is 200.

30% of 500 = 150. 40% of 800 = 320. 150 + 320 = 470.

1989 + 249 - 1998 = 2238 - 1998 = 240.

198.1 * 2.5 = 495.25. The closest approximate value is 500.

Calculate the terms: 5% of 90 is 4.5, 20% of 149 is 29.8, and 79% of 498 is approximately 0.8 * 500 = 400. Then 4.5 + 29.8 - 393.42 = -359.12, which is closest to -365.

(1.2)^2 * (3.5)^2 = (1.2 * 3.5)^2 = (4.2)^2 = 17.64. The closest approximate value is 17.6.

25% of 50% of 19500 = 0.25 * 0.5 * 19500 = 0.125 * 19500 = 2437.5. The options are squares. 50^2 = 2500, which is the closest approximate value.

50% of 339 is 169.5. 25% of 25 is 6.25. 169.5 + 6.25 = 175.75, which is approximately 175.

15% of 680 = 102. 20% of 220 = 44. 102 + 44 = 146. 145 is the closest approximation.

1586 - 81 + 96 + 259 = 1860. 1860 = ? + 25. ? = 1835.

0.99% of 3596 is approx 1% of 3600 = 36. 0.49% of 4802 is approx 0.5% of 4800 = 24. Sum = 36 + 24 = 60.