Use an arithmetic sequence to find how many multiples of 7 are between 36 and 391? How do I do this?

Question

basic equation is
an = a1 + (n-1)d
are we suppose to use it at all in this problem? How do I do it?

Answer 1

First term of the AP is 42 Last term is 385.

So 42 + (n-1)7 = 385
Solve for n

Answer 2

the first multiple of 7 greater than 36 is 42.and the multiple of 7 less than 391 is 385.You now have an arithmetic sequence with first term a1=42 common difference d=7 and the last term l=385.you have to find the number of terms n using the fact that the nth term is the last and the formula for nth term is the basdic equation you have given.we get 385 = 35+(n-1)7 which gives n=51.this is the number of multiples required.

Answer 3

36 = 1 + 5(7)
386 = 1 + 55(7)
391 = 1 + 55(7) + 5 (not enough for another multiple of 7)

55-5 = 50 multiples of 7