Maths

posted by .

Mrs Smith pays kate for babysitting by giving her 10 cents for the first-half hour, 20 cents for the second half-hour, 40 cents for the third half-hour etc. How long does she work to earn \$12.70?

• Maths -

1st half-hr = 10 cents = 5*2^1.

2nd half-hr = 20 cents = 5*2^2.

3rd half-hr = 40 cents = 5*2^3.

t = 5*2^n = 1270 cents.
5*2^n = 1270,
Divide both sides by 5:
2^n = 254,
nlog2 = log254,
n = log254 / log2 = 7.99 half-hrs =
3.99 hrs or 4 hrs.

Similar Questions

1. Chemistry

Assume electricity cost 15 cents kw per hour....using the energy requirements.what is the per gram cost of energy to produce Na + AL?
2. Math

I have a question: How would you solve this?
3. Quick Math

I have a question: How would you solve this?
4. math !!!! :O

Emily’s dad pays her for picking strawberries. Each hour she works he increases her pay. The first hour she earns two cents, the second hour she earns four cents, the third hour eight cents, and so on, doubling the amount each hour. …
5. math !!!! :O

The cost of making money varies form coin to coin: Pennies: 0.8 cents each Nickels: 2.9 cents each Dimes: 1.7 cents each Quarter: 3.7 cents each Half dollars: 7.8 cents each What is the cost of making \$5.00 worth of each coin?
6. Math

A plumber makes \$4.50 per hour more than his apprentice. During an 8-hour day, their combined earnings total \$372. How much does each make per hour?
7. maths

Water is leaking out of a barrel. In the first hour, it lost half the number of litres it held, plus one litre. In the second hour, it lost half the remainder plus another litre. In the third hour, it lost half the remainder again, …
8. math

a parking lot charges 1.50 for the first hour of parking and 55 cents for each additional half hour. How much would it cost to park a car from 12:45 pm to 6:15 pm
9. math

a parking lot charges \$1.50 for the first hour of parking and 55 cents for each additional half hour how much would it cost to park a car from 12:45pm to 6:15 pm
10. maths

A box of 12 table costs 21 cents.The same brand is packaged in bottles containing 100 tablets and sells for \$1.50 per bottle.How much is saved per dozen, by purchasing the larger amount?

More Similar Questions