Barbie and Woody go from school to a swimming pool, starting at the same time. Barbie walks at 70 meters per minute and
Woody cycles 3 times as fast as Barbie walks. 9 minutes later,
Woody arrives. How many minutes earlier than Barbie does
Woody arrive?

Woody arrived  

27 -  9 =  18  minutes before Barbie did.

Step-by-step explanation:

When you are working with Distance=speed-time problems remember that if you know two of the values you can calculate the third one,

Barbie: She walks at a speed of  70  metres per minute.  

Woody: Cycles  3  times as fast:   →3 × 70 = 210 m/min

He cycled for  9  minutes.

210 m/min is his speed.

9  minutes is the time he took.

Distance  =  speed  ×  time

D  =  210  × 9   =  1890  metres,

Barbie: walked the same distance of  1890  metres

Her speed was  70  m/min

The time she took:  

Time=

T i m e  =   =  27  minutes.

Woody arrived  27  −  9  =  18  minutes before Barbie did.

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places