find the sum of the first 25 positive multiples of 4

Question

anonymous · Answer

4 + 8 + 16 + 20 + 24 + 28 + 32 + 36 + 40 + 44 + 48 + 52 + 56 + 60 + 64 + 68 + 72 + 76 + 80 + 84 + 88 + 92 + 96

= 4 + (4 + 4) + (4 + 4 + 4) + ...

= take a triangular number to the 25th row and multiply that by 4

anonymous · Answer

i still dont understand

raden · Answer

first, the 25th term is 
4 * 25 = 100

so, the series is
4 + 8 + 12 + 16 + ... + 100

use the Gauss rule :
let 
A = 4 + 8 + 12 + 16 + ... + 100
A = 100 + 96 + 92 + ... + 8 + 4
------------------------------ (+)
2A = 104 + 104 + 104 + ... + 104
2A = 25 * 104
now you can solve for A, right ?

anonymous · Answer

2600

anonymous · Answer

then divid it by 2 an u get 1300

raden · Answer

yeah, it is 1300