Arithmetic Progression III

Number Theory Level 1

35 , . . . , 125 , . . . 215... 35,...,125,...215...

In the above AP the Common Difference is 10.

125 and 215 are respectively:

60th and 80th term 30th and 40th term 10th and 19th term 11th and 20th term

Victor Paes Plinio by Victor Paes Plinio , 21, Brazil

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4 solutions

The formula used is:- tn = a + ( n - 1 ) * difference

Where tn = term number , a = first number of the sequence

Tn = a + ( n - 1 ) * difference

= 35 + 10n -10

= 10n + 25

We have got the formula and have to find the positions.

125 = 10n + 25

100 = 10n

n = 10

215 = 10n + 25

190 = 10n

n = 19

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Good soluction

Heder Oliveira Dias - 6 years, 11 months ago

by using nth term=a+(n-1)d

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Tasnia Nowrin
Jul 10, 2014

125 - 35=90 /10=9

since we need to count from 35 so the position for 125 is

(9+1)=10;

215 -35=180/10=18

so the position of 215 is 19

0 Helpful 0 Interesting 0 Brilliant 0 Confused
Dhaval Furia
Apr 22, 2014

nth term = first term + ( n - 1 ) * common difference

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