Foundation June 2019 Paper 3 Q17
17 A grain of salt weighs \(6.48 \times 10^{-5}\) kg on average.
A packet contains 0.35 kg of salt.
(a) Use this information to calculate the number of grains of salt in the packet. [2]
(b) Explain why your answer to part (a) is unlikely to be the actual number of grains of salt in the packet. [1]
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| 5400 or 5401 or 5402 final answer | 2 | M1 for figs \(35 \div\) figs 648, soi by figs 540[1…] or for 0.0000648 seen | |
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| Any reference to average/inexact weight oe [in packet weight or weight of a grain] or recognising that the number of grains of salt must be integer oe | 1 | Condone any mention of
See appendix | |
Appendix
Question 17b
| Response | Mark | |
|---|---|---|
| A | Because it is a decimal and you can’t have a decimal of a grain of salt. | 1 Reference to requiring integer value |
| B | They might have rounded the 0.35kg up. | 1 Equivalent to “figures not exact” |
| C | Some grains can be lighter or heavier than this. | 1 “this” is “the average”? |
| D | The weight of each grain is an average. | 1 True; mention of average |
| E | The weight given is an average weight. | 1 True; mention of average |
| F | As it is an average amount of salt. | 1 True; mention of average. Read amount for weight |
| G | Some grains of salt may be heavier. | 1 Implies variation |
| H | It’s an average | 1 Minimum case |
| I | It’s not exact | 1 Minimum case |
| J | It’s a decimal | 1 Minimum case |
| K | Because it is hard to exactly measure that finite amount consistently. | 0 It may be “hard to measure” but doesn’t say they are not exact. |
| L | It’s an estimate because in some packets there will be slightly more or less grains as they are too small to count. | 0 Refers to the number of grains and does not reference the weight of a grain. |
| M | There could be a fraction of a grain of salt. | 0 Implies number of grains can be non-integer. |
| N | They all weigh the same but could be different sizes | 0 Choice One incorrect statement and one correct |