(b) The average mass of 4 boys is 45kg. When a fifth boy joins them, the avaerage mass
changes to 40kg. What is the mass of the fifth boy?
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Answer:
20 kg
Step-by-step explanation:
mass of all 4 boys = x/4 = 45
x = 4 * 45 = 180
let the mass of fifth boy be y
180+y/5 = 40
y = 20
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