Video Transcript
The average person blinks about 900 times an hour. By rounding the number of hours in a day to the nearest 10, estimate how many times a person blinks in a day. Is this estimate more or less than the actual number of times a person blinks in a day?
This problem starts off with a fact. The average person blinks about 900 times an hour. The question asks us to estimate the number of times that a person blinks in a day. The first thing to remind ourselves is the number of hours in a day. One day is equal to 24 hours. But the method that we need to use to estimate the number of times a person blinks in a day is to round the number of hours to the nearest 10. Rounding numbers to the nearest 10 makes them easier to deal with. The two multiples of 10 either side of 24 are 20 and 30. So 24 is somewhere in between 20 and 30. We know the half way point between 20 and 30 is 25. And so 24 will be somewhere around here. So is the nearest 10 to 24 20 or 30?
We can see that 24 is nearest to 20. When a number ends in a four, we round it down. So to find our estimate, we need to use the number 20 and not 24. The average person blinks about 900 times an hour. And so to estimate the number of times that somebody blinks in a day, we need to multiply this by our rounded number, which we said was 20. And we just need to find the answer to the calculation 900 multiplied by 20. Can you see a number fact that we could use to help us here? We know nine times two equals 18. And so 900 multiplied by two equals 18 hundreds or 1800. And so 900 multiplied by 20 means we have to multiply 1800 by another 10. The answer is 18000. By rounding the number of hours in a day to the nearest 10, we made the calculation a lot quicker to work out.
Now, we just have to answer the final question. Is this estimate more or less than the actual number of times a person blinks in a day?
To work out our estimate, we multiplied 900 by 20. To find the actual number of times a person blinks in a day, we need to multiply the number of times they blink in an hour, which we said was 900, by the number of hours in a day. This is 24. Look at these two multiplications. Is the estimate going to be more or less than the actual number of times a person blinks in a day? Well, 20 is less than 24. So 900 times 20 is going to be less than 900 times 24. Our estimate is less than what we’d expect the actual answer to be. There are 24 hours in a day, but we rounded this number to the nearest 10 which we said was 20. And we use this to help us estimate the number of times of the person blinks in a day. 900 multiplied by 20 equals 18000 times. And because we rounded 24 down to 20, the estimate was less than the actual number of times a person blinks in a day.
