CPhill

Here's another way to do the first one

y = (x^1/2  - 3 ) (x^1/2 - 4)   =  ( x - 7x^1/2 + 12)

And differentiating term by term  we have

1 - (7/2)x^-1/2

So

y ' (1)   =  1 - 7/2   =  -5/2

78/9 : 2/3 = 12 ?

Substituting, we have

13 / 1  = 12 / ?   cross-multiply

13?  = 12     divide both sides by 13

?  = 12/ 13

3^x=29   take the log of each side

log 3^x = log 29   and we can write

x log 3  =  log  29     divide both sides by log 3

x = log 29 / log 3   =  about  3.065

Here's a calculator that will do this for you......http://www.alcula.com/calculators/statistics/standard-deviation/

You must specify whether this is a population or a sample.....the results are different, depending upon the assumption....

(3 /40) * 360°  =

360° / 40  * 3 =

9° * 3  =

27°

Thanks for that answer, Guest....here's another way to see this.......if the crew can mow 45 lawns in 10 hours, each hour they must mow 1/10 of this =  4.5 lawns

So........

4.5 lawns per hour :  9 workers  =  [ 1/2 ] lawn per hour : 1 worker

Omi has assumed that both figures have the same area....that's not expressly stated in the problem, but it might be true..........if not.......Melody's answer is the more general one.......

28 ( 1 + .0725)  = $30.03

This is Fahrenheit

Celsius = (F - 32) (5/9)   = [70 - 32] (5/9)  = [ 38](5/9)  about 21.1° C

Kelvin =  [ F - 32 ] (5/9) + 273.15  =  [ 70 - 32] (5/9) + 273.15  = about 294.26° K

This is just a linear equation

-7h-5=4-4h      add 7h to both sides, subtract 4 from both sides

-9  = 3h       divide  both sides by 3

-3 = h