100 kg of a fruit contained 90% water one week ago. how many kg of the fruit containing 80% water are there now?

90kg 

It is just a simple proportional problem. If you subtract 10%, then you subtrat 10 kg. 

2.5 seconds The acceleration due to gravity is about 32 ft/s^2. So formula for distance under constant acceleration and with an initial velocity is: d = VT - 0.5 AT^2 where V = initial velocity T = time A = acceleration due to gravity. Substituting known values and solving for T gives -20 = 32 ft/s * T - 0.5 * 32 ft/s^2 * T^2 -20 = 32 ft/s * T - 16 ft/s^2 * T^2 0 = 32* T - 16 * T^2 + 20 -16T^2 +32T +20 = 0 And we now have a quadratic equation with A=-16, B = 32, C = 20. Use the quadratic formula to find the roots, which are -0.5 and 2.5. The -0.5 root would be what happened if you managed to go back in time 0.5 seconds, dig underground 20 feet and hit the ball. But we'll ignore that and use the 2.5 time instead. So the ball lands on the ground 2.5 seconds after being hit.