A man Saves #100.00 in his first year of work and each year saves #20.00 more than the preceding year. In how many years will he save #5800.00?

Cunnyguy

3 years ago

A man Saves #100.00 in his first year of work and each year saves #20.00 more than the preceding year. In how many years will he save #5800.00?
Answer 👇
What he saved first called first a=100

Common different d=20

Sum of the last term Sn=5800

Using the formular Sn=n/2(2a+(n-1)d)

5800=n/2(2(100)+(n-1)20)

5800=n/2(200+20n-20)

5800=n/2(180+20n)

Divide the bracket by 2

5800=n(90+10n)

Factories 10 out

5800=10n(9+n)

Divide through by 10

580=n(9+n)

580=9n+n^2

n^2+9n-580=0

n^2+29n-20-580=0

n=20