Find stamps

Question

John, Mei and Kim collect stamps. John and Mei have 220 stamps more than Kim. Kim and Mei have 140 more stamps than John. John and Kim have 500 stamps. How many stamps does Mei have?

Answer 1

j=# stamps John has

m=# stamps Mei has

k=# stamps Kim has

 

j+m=k+220

k+m=j+140

j+k=500

 

j-k=-m+220 from equation1

-j+k=-m+140 from equation2

add

0=-2m+360

2m=360

m=180 stamps for Mei (answer)

 

for the rest of the problem...

j+180=k+220

j+k=500

j-k=220-180

j+k=500

j-k=40

j+k=500

add

2j=540

j=270 (John)

 

270+k=500

k=500-270

k=230 (Kim)