Posted by **Annabella Richards** on Monday, June 20, 2011 at 2:10am.

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 -
**Henry**, Monday, June 20, 2011 at 4:20pm
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.

## Answer This Question

## Related Questions

- math !!!! :O - Emily’s dad pays her for picking strawberries. Each hour she ...
- Math - A plumber makes $4.50 per hour more than his apprentice. During an 8-hour...
- math - a parking lot charges 1.50 for the first hour of parking and 55 cents for...
- math - a parking lot charges $1.50 for the first hour of parking and 55 cents ...
- Math - I have a question: How would you solve this? a dozen dozen apples at half...
- maths - Water is leaking out of a barrel. In the first hour, it lost half the ...
- Quick Math - I have a question: How would you solve this? a dozen dozen apples ...
- Chemistry - Assume electricity cost 15 cents kw per hour....using the energy ...
- maths - A box of 12 table costs 21 cents.The same brand is packaged in bottles ...
- math !!!! :O - The cost of making money varies form coin to coin: Pennies: 0.8 ...

More Related Questions