Question

49. A child puts one five-rupee coin of her savings in the piggy bank on the
first day. She increases her saving by one five-rupee coin daily. If the
piggy bank can hold 190 coins of five rupees in all, find the number of
days she can contribute to put the five-rupee coins into it and find the
total money she saved.
[CBSE 2017]​

Answer 1

Answer: Rs. 90725

The child puts in her piggy bank on first day = Rs. 5 coin  

On second day she puts = 5 + 5 = Rs. 10  

On third day she puts = 5 + 5 + 5 = Rs. 15

Her piggy bank can hold 190 5 rupee coin in all.

So, this is the case of an Arithmetic Progression.

5, 10, 15, ......................190

a = 5, d = 5 and n = 190

S = n/2[2a + (n - 1)d]

⇒ 190/2[2*5 + (190 - 1)5

⇒ 95[10 + 189*5]

⇒ 95[10 + 945]

⇒ 95*955

= Rs. 90725

Her total saving is Rs. 90725