+0  
 
0
15
1
avatar+12 

On his outward journey, Ali travelled at a speed of skm/h for 2 1/2  hours. On his return journey he increased his speed by 4 km/h and saved 15 minutes. Find Ali's average speed for the whole journey.

 Oct 11, 2023
 #1
avatar+128732 
+1

Rate * Time =  Distance

 

Call the outward rate =  S

Call the inward rate  S+ 4

 

So

 

S( 2.5 hrs)  = (S + 4) (2.25 hrs)

 

2.5 S  =  2.25S + 9

 

2.5S - 2.25S  = 9

 

.25S  =  9

 

S  = 9 / .25  =   36  km/h

 

S + 4  =  40km/h

 

The avg rate  =    2 ( product of the rates)  / ( sum of the rates)  = 

 

2 (36 * 40) / ( 36 + 40)  =

 

2 (1440) / ( 76)  ≈  37.9 km/h  

 

 

cool cool cool

 Oct 11, 2023

6 Online Users

avatar
avatar
avatar