PSLE
Four girls, Abi, Jen, Betty and Rachel raised money for a charity. Abi and Jen raised a total of $80. Together, Jen, Betty and Rachel raised a total of $128. The total amount of money raised by all 4 girls is 3 times the amount that Jen raised. How much money did Abi raise?
Amount that Jen and Abi raised = $80
Amount that Jen, Betty and Rachel raised = $128

Jen is the repeated identity.

Jen + Abi = 80 --- (1)
Jen + Betty + Rachel = 128 --- (2)

Amount that Jen raised = 1 u
Amount that 4 girls raised = 3 u

(1) + (2)
(Jen + Abi) + (Jen + Betty + Rachel) = 80 + 128
Jen + 4 girls = 208
1 u + 3 u = 208
4 u = 208

1 u = 208 ÷ 4 = 52

Amount that Abi raised
= 80 - 1 u
= 80 - 52
= $28

Answer(s): $28