1.1TEEHow many terms of the series 42, 36, 30.....amount to 150 ?

1.	1.1TEEHow many terms of the series 42, 36, 30.....amount to 150 ?
Answer» Formula: Sn(Sum of nos. till nth term)=n/2(2a+(n-1)d) Here: First term ‘a' is 42. Difference ‘d' is -6. Sn =150 Substituting values in the equation: 150=n/2(242+(n-1)8(-6)) 300=n(84+(n-1)*-6) 300=n(84-6n+6) 300=90n+6n² Dividing equation by 6: 50=15n+n² n²+15n-50=0 Solving for n we get: n=5 and some negative answer. But n cant be negative so,n=5 So the number of terms is 5.

Answer»

Formula:

Sn(Sum of nos. till nth term)=n/2(2a+(n-1)*d)

Here:

First term ‘a' is 42.

Difference ‘d' is -6.

Sn =150

Substituting values in the equation:

150=n/2(2*42+(n-1)8(-6))

300=n(84+(n-1)*-6)

300=n(84-6n+6)

300=90n+6n²

Dividing equation by 6:

50=15n+n²

n²+15n-50=0

Solving for n we get:

n=5 and some negative answer.

But n cant be negative so,n=5

So the number of terms is 5.

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