A baby snake which is 10 cm long grows longer by 2 cm on the first day, 4 cm on the second day, 6 cm on the third day, 8 cm on the fourth day and so on. If it continues to grow at this rate, how many days will it take to grow to a length of 1.2 m?
Length of the snake
Day 1: 10 + 2 = 10 + 2 x (1)
Day 2: 10 + 2 + 4 = 10 + 2 x (1 + 2)
Day 3: 10 + 2 + 4 + 6 = 10 + 2 x (1 + 2 + 3)
Day 10: 10 + 2 + 4 + 6 + 8 = 10 + 2 x (1 + 2 + 3 + 4)

Formula:
Length of the snake = 10 + 2 x {[Day Number x (Day Number + 1)] ÷ 2}

1 m = 100 cm
1.2 m = 1.2 x 100 = 120 cm

10 + 2 x {[(Day Number) x (Day Number + 1)] ÷ 2} = 120
10 + [(Day Number) x (Day Number + 1)] = 120
Day Number x (Day Number + 1) = 120 - 10 
Day Number x (Day Number + 1) = 110
10 x 11 = 110

Number of days for the snake to grow to a length of 1.2 m = 10

Answer(s): 10