Question

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Answer 1

1)

from given condition

A.P is 12,16,20,......248

here, a=12, d=4, tn=248

tn= a+(n-1) d

248 =12 + (n-1) 4

248 = 12+ 4n-4

248 = 8+4n

248-8 = 4n

240 = 4n

240/4 = n

60

Ans: there are 60 multiples.

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2) here, a= 3, d= 5 and tn= 253

n = ?

tn = a+(n-1)d

253 = 3 + ( n-1) 5

253 = 3+ 5n-5

253 = -2+5n

253+2 = 5n

255 = 5n

n = 51

Ans : number of term is 55.

Answer 2

Answer:

And your 3rd answer is here

Two digit numbers of 3 are started form 12 and that series are 12,15,18,.........,999

Here a=12, d=15-12=3 and an=999

formula is an =a +(n-1)d

999=12+(n-1)3

333=12+(n-1)

333-12=(n-1)

321=(n-1)

n=322

Hope this is helpful