1a:
580 - (580 × .1) - 20
580 - (58) - 20
522 - 20
502
1b:
990 - (990 × .25) - 20
990 - (247.5) - 20
742.5 - 20
722.5
I'm not sure how to solve #2.
Answer:
The altitude to the base of an isosceles triangle bisects the vertex angle of the triangle.
Step-by-step explanation:
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Step-by-step explanation:

Here is a method that makes it seem easier.
<span>Write down any number between 51 and 59. </span>
<span>For example you might choose 57 = 3*19 </span>
<span>Divide both numbers by 10 and write the answer as </span>
<span>0.3 * 1.9 = 0.57</span>