Let's use the letters:
• C for the number of classmates at the party,
,
• S for the number of friends from summer camp at the party,
,
• R for the number of relatives at the party.
So, the total number of people at the party is:
C + S + R
We ere already informed that the number of classmates is 5. So:
C = 5
Also, we know that 5 is half as many as the number of friends from his summer camp. So:
5 = S/2
Multiplying both sides of the relation above, we find:
2 * 5 = 2 * S/2
10 = S
S = 10
Now, we also know that 5 is one-third as many as the number of his relatives that were there. So, we have:
5 = R/3
3 * 5 = 3 * R/3
15 = R
R = 15
Therefore, the total number of people at the party is:
C + S + R = 5 + 10 + 15 = 30
Answer: There were 30 people at Dan's birthday party.