Hello everyone. I'd like to discuss using estimation as a test taking strategy. This is one of my favorites, but one some students that I encountered did not willingly embrace. Some of the complaints were that it was extra work, or that they were not careful enough with the estimation. I believe they may have had bad experiences in the past with estimation and rounding, as it has a few arbitrary rules that they may have been caught up in.
Estimation is a vital skill that we use every day whether we know it or not. When we're out shopping, we estimate prices all the time. 19.95 becomes 20 very quickly. This in turn, helps us calculate and budget how much should be spent on each item. It also helps us compare prices, especially when the stores don't want to give out cost per unit. 3.99 for 10 apples for example versus 0.67 for 1 apple.
Where students seem to be falling down is that they don't understand when to estimate, or what information the estimate gives us, thus why it's useful. Estimation is especially useful on problems that involve measurement, as they nearly all include multiplication, sometimes multiple step multiplication. Thus, having an easier set of multiplication to do can eliminate answers, perhaps even enough answers that the correct one is left alone.
Estimation gives us minimums and maximums. In my example above, the maximum it will be is $20. Then estimating tax of 10% gives us tax of $2, so we should have $22 ready to spend at the register for our item that costs $21.64 exactly. Thus, we got a maximum price, exceeded it so that we would get change back instead of having to leave without the item.
Likewise with measurement. We should estimate close to the measurements given but make sure we always round down to get our minimum, then always round up to get our maximum. This strategy can help students who are not careful with decimals when they multiply. Students who know their multiplication facts will also find that estimation is much faster than multiplying the decimals out. Other things to point out would be when a number is very close to an easy multiplication fact, like 2, 5, or 10.
The problem with this strategy, when the test is really mean, is that it is possible that it will not eliminate enough answers and a guess or the long multiplication is still required. In that case, remind students that their exact answer will fall between their minimums and maximums. Looking at the entire question including the answers would be the best idea to determine if they should estimate or not. If the numbers vary greater than 3-4, estimation will eliminate 1-2 answer choices and possibly all 3 of the wrong ones.
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