This year, christie has 15 fish in her tank. she has one
fish fewer than twice the number she had last year.
how many fish did she have last year?

15x2-1=29

she has 29 fish last year.

Step-by-step explanation:

The solutions for 1 + 3 + 5 +...+ (2n - 1), for the first 10 natural numbers are given in the explanation section below.

Step-by-step explanation:

To calculate 1 + 3 + 5 +...+ (2n - 1) for several natural numbers n, we will use several natural numbers to represent n.

For n= 1,

2n - 1 = 2(1) - 1 = 2 - 1 = 1

Hence, 1 = 1

For n = 2,

2n - 1 = 2(2) - 1 = 4 - 1 = 3

Hence, 1 + 3 = 4

For n = 3,

2n - 1 = 2(3) - 1 = 6 - 1 = 5

Hence, 1 + 3 + 5 = 9

For n = 4,

2n - 1 = 2(4) - 1 = 8 - 1 = 7

Hence, 1 + 3 + 5 + 7 = 16

For n = 5,

2n - 1 = 2(5) - 1 = 10 - 1 = 9

Hence, 1 + 3 + 5 + 7 + 9 = 25

For n = 6,

2n - 1 = 2(6) - 1 = 12 - 1 = 11

Hence, 1 + 3 + 5 + 7 + 9 + 11 = 36

For n = 7,

2n - 1 = 2(7) - 1 = 14 - 1 = 13

Hence, 1 + 3 + 5 + 7 + 9 + 11 + 13 = 49

For n = 8,  

2n - 1 = 2(8) - 1 = 16 - 1 = 15

Hence, 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 = 64

For n = 9,

2n - 1 = 2(9) - 1 = 18 - 1 = 17

Hence, 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 = 81

For n = 10,

2n - 1 = 2(10) - 1 = 20 - 1 = 19

Hence, 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 = 100