Math  /  Algebra

QuestionHenrietta managed a plantation of pine trees which were grown and sold for their timber. The plantation was developed from an initial planting of 45000 trees, with a net increase, after sales and plantings, of 2500 trees each year over a period of 15 years. At the beginning of the 16 th year of the plantation, it was decided to sell-off 40%40 \% of the trees remaining on the plantation each year for timber, without any further plantings, so that the land could ultimately be used for another purpose. Questions:
1. How many trees were on the plantation at the beginning of the 5 th year of the plantation?
2. At the beginning of which year of the plantation there were 65000 trees on the plantation?

Studdy Solution

STEP 1

1. The initial number of trees is 45,000.
2. The net increase in the number of trees each year is 2,500.
3. The period of net increase is 15 years.
4. From the 16th year onwards, 40% of the trees are sold off each year without any further plantings.
5. We need to find the number of trees at the beginning of the 5th year.
6. We need to determine the year when the number of trees reaches 65,000.

STEP 2

1. Calculate the number of trees at the beginning of each year up to the 5th year.
2. Determine the year when the number of trees reaches 65,000.

STEP 3

Calculate the number of trees at the beginning of the 1st year. N1=45000 N_1 = 45000

STEP 4

Calculate the number of trees at the beginning of the 2nd year. N2=N1+2500=45000+2500=47500 N_2 = N_1 + 2500 = 45000 + 2500 = 47500

STEP 5

Calculate the number of trees at the beginning of the 3rd year. N3=N2+2500=47500+2500=50000 N_3 = N_2 + 2500 = 47500 + 2500 = 50000

STEP 6

Calculate the number of trees at the beginning of the 4th year. N4=N3+2500=50000+2500=52500 N_4 = N_3 + 2500 = 50000 + 2500 = 52500

STEP 7

Calculate the number of trees at the beginning of the 5th year. N5=N4+2500=52500+2500=55000 N_5 = N_4 + 2500 = 52500 + 2500 = 55000

STEP 8

Set up the equation for the year k k when the number of trees reaches 65,000. Nk=45000+(k1)×2500 N_k = 45000 + (k-1) \times 2500

STEP 9

Solve for k k when Nk=65000 N_k = 65000 . 65000=45000+(k1)×2500 65000 = 45000 + (k-1) \times 2500

STEP 10

Simplify the equation to solve for k k . 6500045000=(k1)×2500 65000 - 45000 = (k-1) \times 2500 20000=(k1)×2500 20000 = (k-1) \times 2500 k1=200002500 k-1 = \frac{20000}{2500} k1=8 k-1 = 8 k=9 k = 9
The number of trees at the beginning of the 5th year is 55,000.
The number of trees reaches 65,000 at the beginning of the 9th year.

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