What is the seventh term of the arithmetic progression 2 , 7 , 1 2 , 1 7 , … ?
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Common difference is 5 .
2 + 6 ( 5 ) = 3 2
Look at it in pairs. _2 is always odd so 7th is _2. 1&2, 3&4 share the tens digit, so 7&8 also share the tens digit. The tens digit is the 2nd number in a pair divide by 2 and minus 1. Therefore, the answer is 7.
We have that: a n = a 1 + d ( n − 1 )
To get a 1 , we just choose the first number of our series, that in 2 , 7 , 1 2 , 1 7 , . . . , is 2 .
So, we get that a 1 = 2
Then, to get d , we could calculate the difference of two consecutive numbers using the formula ( a n + 1 − a n ) .
For example: ( 7 − 2 = 5 ) , and if we want to corroborate, we could just repeat it with some different consecutive numbers, like ( 1 2 − 7 = 5 ) or ( 1 7 − 1 2 = 5 ) .
So, we get that d = 5
Finally, to get n , we just check the text, and it says that we need to know the seventh term.
So, we get that n = 7
Now, we can substitute on our main formula:
a n = a 1 + d ( n − 1 ) a n = 2 + 5 ( 7 − 1 ) a n = 2 + 3 0 a n = 3 2
The nth term of an arithmetic progression is:-
t n = a + ( n − 1 ) d where a is the first term, and d is the common difference.
Putting n=7, we get it as 32.
Shouldn't the answer be 22 as this equation has a linear progression?
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The answer would be 22 if the question asked for the 5th term, but it asked for the 7th term of this linar progression
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nth term is 7 and initial number is 2 and common difference in sequence is 5,so we know the formula tn=a1+d(n-1) Put the value in this, t7=2+5(7-1)=32 t7=32