Question 11

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Jambmaths question: 

A man saves N100.00 in his first year, saves N20.00 more than in the preceding year. In how many years will he save N5,800.00

Option A: 

100yrs

Option B: 

58 yrs

Option C: 

29 yrs

Option D: 

20yrs

Jamb Maths Solution: 

$\begin{align}& a=100,\text{ }d=20,\text{ }{{S}_{n}}=5800 \\ & {{S}_{n}}=\tfrac{n}{2}\left[ 2a+(n-1)d \right] \\ & 5800=\tfrac{n}{2}\left[ 2(100)+(n-1)20 \right] \\ & 11600=n\left[ 200+20n-20 \right] \\ & 11600=180n+20{{n}^{2}} \\ & {{n}^{2}}+9n-580=0 \\ & (n+29)(n-20)=0 \\ & n=-29\text{ or }n=20 \\\end{align}$n cannot be negative, so we ignore n = – 29  and accept n = 20

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