For this problem,we use the Fundamental Counting Principle. You know that there are 7 digits in a number. In this principle, you have to multiply the possible numbers for every digit. If the first number cannot be zero, then there are 9 possible numbers. So, the value for the first digit is 9. The second digit could be any number but less of 1 because it was used in the 1st digit. So, that would be 10 - 1 = 9. The third digit must be the value in the second digit less than 1. That would be 9 - 1 = 8. And so on and so forth. The solution would be:
9×9×8×7×6×5×4 = 544,320 7-digit numbers
215,000 x 5.2% =11,180 quarterly compounded interested
quarter = 4 theres 4 quarters in a year
3years x 4 quarters= 12 quarters
12 quarters x 5.2% of 215,000 =
134,160(compounded interested)+ 215,000(money he owes) =
349,160
The light's coverage area is given mathematically as i.e. Area=
Given that a lighthouse casts a revolving beam of light as far as they peir and asked the area is covered.
The revolving beam of light covers the whole space i.e entirely 360°
I.e. it forms a circle-like region
Area of circle = 
{ where r is the radius of circle}
Let's assume the distance traveled by light as "d"
as it forms a circular region, it forms a circle of radius "d"
Mathematical connection i.e. area of the region
⇒area of circular region= {where d is the radius of region}
Learn more about area here:
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2x + 3y = 10 -> y = -2/3x + 10/3 it's a function
4x = 16 -> x =4 it's not a function
2x - 3 = 14 -> x = 8.5 it's not a function
3y = 18 -> y = 6 it's a function
2x = 6 -> x = 3 it's not a function
(32ft/s)(60s/min)(yd/3ft)=640 yds
