Betty had 3440 red, yellow and blue beads. The number of red and yellow beads that Betty had was equal.

After using only some yellow and blue beads to make a necklace, she had 5/7 of yellow beads and 3/5 of blue beads left.
Given that the number of beads left was 2820, how many blue beads did she have at first?
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3/5 of the pupils at a camp were girls. After 12 girls and 4 boys left the camp, the ratio of the number of girls to the number of boys became 4:3.

How many pupils were at the camp at first?
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Jane bought a total of 55 cupcakes and mini buns for a party.

Each cupcakes cost $3.60 and each mini bun cost $1.40.
Jane spent a total of $151.80. How many cupcakes did Jane buy???