Answers

2015-03-08T18:32:59+05:30
He donates money for 
        from 1 to 10th day he donated 55 rs 
        from 11th to 20 th day he will haven donated 210 rs
explanation 
 on 1st day 1 2nd 2 and so on 
 1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=210 
1 1 1
This can be easily solved using A.P
we have, a = 1, d = 1, Sn = 210. Put these value in formula Sn = n/2[2a + (n-1)d], where n is no. of day.
The Brainliest Answer!
2015-03-08T19:34:37+05:30
Money=210
sn=210
it is in ap form
f=1
d=1
sn= \frac{n}{2} [2f+(n-1)d] \\
 210*2=n[2+n-1)] \\ 
420=n(1+n) \\ 
n ^{2}+n=420  \\ 
n ^{2} +n+0.25=420.25 \\ 
(n+0.5) ^{2} =420.25
n+0.5=20.5
n=20
he donates in 20 days
2 5 2