# Time + exponential equation - math problems

#### Number of problems found: 26

• Compound interest
Calculate time when deposit in the bank with interest 2.5% p.a. doubles.
• Car value
The car loses value 15% every year. Determine a time (in years) when the price will be halved.
After 548 hours decreases the activity of a radioactive substance to 1/9 of the initial value. What is the half-life of the substance?
• What is
What is the annual percentage increase in the city when the population has tripled in 20 years?
• RC time constant
You introduced 1 Coulomb worth of electrons into the inner volume of a dielectric material with ϵr=6. 30 minutes later, you found that only 36.79% of the electrons were in the inner volume. Determine the conductivity σ of the dielectric material.
• Demographics
The population grew in the city in 10 years from 30000 to 34000. What is the average annual percentage increase of population?
• Water lilies
Water lilies are growing on the pond and their number is doubled every day. The whole layer is covered in 12 days. How many days will it cover 8 layers?
• Exponential warm
Suppose that a body with temperature T1 is placed in surroundings with temperature T0 different from that of T1. The body will either cool or warm to temperature T(t) after time t, in minutes, where T(t)=T0 + (T1-T0)e^(-kt) . If jello salad with 30 degree
• An investment
How long will it take for an investment to double at a simple interest rate of 5.10% p. A. ? Express the answer in years and months, rounded up to the next month.
• Half life
Determine the half life of bismuth, when bismuth weight from the original weight of 32 g was only 2 grams in 242 minutes.
• Growth of wood
The annual growth of wood in the forest is estimated at 2%. In how many years will make the forest volume double?
• If you 4
If you deposit \$2500 in an account paying 11% annual interest compounded quarterly, how long until there is the \$4500 in the account?
• Six speeds
A drilling machine is to have 6 speed ranging from 50 to 750 revolution per minute. If the speed forms a geometric progression, determine their values.
• If you 2
If you deposit \$4000 into an account paying 9% annual interest compounded monthly, how long until there is \$10000 in the account?
• Compound Interest
If you deposit \$6000 in an account paying 6.5% annual interest compounded quarterly, how long until there is \$12600 in the account?
• Volume of wood
Every year, at the same time, an increase in the volume of wood in the forest is measured. The increase is regularly p% compared to the previous year. If in 10 years the volume of wood has increased by 10%, what is the number p?
• Annual growth
The population has grown from 25,000 to 33,600 in 10 years. Calculate what was the average annual population growth in%?
• Crystal
The crystal grows every month 1.2 permille of its mass. For how many months to grow a crystal from weight 177 g to 384 g?
• Microorganisms
The first generation of micro-organisms has a population of 13500 members. Each next generation is 11/10 times the previous one. Find out how many generations will reach at least three times members of the first generation.
• Exponential decay
A tank contains 55 liters of water. Water is flowing out at the rate of 7% per minute. How long does it take to drain the tank?

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