Weights

Solution

Now 38 is not exactly divisible by 5 or 7. Hence both 5g and 7g weights are needed. Now 38 – 7 = 31, 38 – 2 x 7 = 24, and 38 – 3 x 7 = 17 are not divisible by 5. However, 38 – 4 x 7 = 10 = 2 x 5. So Dr Martin can use four 7g weights and two 5g weights.