Work back method
if each modem costs 1$, then total cost is 4000$. If the cost increases by 25%, then the cost will be 5$
d=4000
Then substitute the value in given options to get an answer of 5$
1. d/800=4000/800=5$
2. 5d/1000= 20,000/1000= 20
3. 125d= NS
4. d/1000+25= 29
5. 125/1000d= NS
Finally answer A
if each modem costs 1$, then total cost is 4000$. If the cost increases by 25%, then the cost will be 5$
d=4000
Then substitute the value in given options to get an answer of 5$
1. d/800=4000/800=5$
2. 5d/1000= 20,000/1000= 20
3. 125d= NS
4. d/1000+25= 29
5. 125/1000d= NS
Finally answer A












