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Jerry started doing sit-ups every day. The first day he did 15 sit-ups. Every day after that he did 4 more sit-ups than he had done the previous day. Today Jerry did 65 sit-ups. Write an equation that could be solved to find the number of days Jerry has been doing sit-ups, not counting the first day. Let n represent the number of days.
Thanks

Respuesta :

The first day Jerry did 15 sit-ups:

a0 = 15

The 2nd day he did 4 more sit-ups then the previous:

a1 = a0 + 4

The 3rd day he did 4 more sit-ups then the previous:

a2 = a1 + 4

a2 = a0 + 4 + 4

a2 = a0 + 4*4

the (n+1)-th day he did:

an = a0 + 4n

Today Jerry did 65 sit-ups means we have: an = 65 and we need to find n

a0 + 4n = 65

15 + 4n = 65

Now to solve

subtract 15 from both sides 

4n = 50

divide both sides by 4

n = 12.5


But I think this is counting the first day

Not counting the first day would be

4n = 65

n = 16.25


I guess that's the answer :)

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