Justin has a total of 16 Singapore and Malaysian stamps.
S + M = 16
If he exchanges every Singapore stamp for 2 Malaysian stamps,
1. He first would subtract the S Singapore stamps, and has left only
M Malaysian stamps
2. Then second, he would replace the S Singapore stamps with 2S
Malaysian stamps.
he will have 21 Malaysian stamps.
3. Then he would have the M Malaysian stamps he had at the start
PLUS the 2S Malaysian stamps he traded for, or M + 2S.
How many Singapore and Malaysian stamps does Justin have?4. We set that quantity equal to 21.
So M + 2S = 21
Solve that for M
M = 21-2S
Substitute 21-2S for M in
S + M = 16
S + (21-2S) = 16
S + 21 - 2S = 16
-S + 21 = 16
-S = -5
S = 5
Substitute 5 for S in
M = 21-2S
M = 21-2(5)
M = 21-10
M = 11
So he has 5 Singapore stamps and 11 Malaysian stamps.
Checking: He has 5+11 stamps, which when added gives 16.
That checks! If he trades the 5 Sinapore stamps for twice
as many, or 10, Malaysian stamps, then he'll have 10 more
Malaysian stamps than the 11 he started with, or 21 Malaysian
stamps. That also checks.
Edwin