Question

charles needs to deliver some parcels. if he works at his usual speed, he can deliver all the parcels in 10 hours. if he delivers 5 more parcels per hour, then he can finish in 8 hours. how many parcels does charles deliver per hour usually?
a 15
b 18
c 20

Explanation:

Step1: Define variables

Let $x$ = usual parcels per hour, $T_1=10$h, $T_2=8$h, extra=5 parcels/h. Total parcels: $10x = 8(x+5)$

Step2: Expand right-hand side

$10x = 8x + 40$

Step3: Isolate $x$ term

$10x - 8x = 40$
$2x = 40$

Step4: Solve for $x$

$x = \frac{40}{2} = 20$

Answer:

C. 20