Three packets of nails weigh 850 g, 1.25kg and 950 g respectively. When a fourth bag is added the mean weight is 975 g. What was the weight of the fourth bag?
Note : 1.25kg = 1250g
[ 850 + 1250 + 950 + W ] / 4 = 975
[3050 + W ] / 4 = 975 multiply both sides by 4
3050 + W = 3900 subtract 3050 from both sides
W = 850 g = weight of 4th bag
