Upthrust on ball = weight of displaced water =Vσg=(
m
ρ
)σg=
40
0.8
×1×g=50g As the ball is sunk into the water with a pin by applying downward force equal to upthrust on it. So reading of weighing pan = weight of water + downward force against upthrust = 600 + 50 = 650 gm