Grades 7-8 Video Solutions 2022-2022_7-8

Video Transcription

Question 10. Gerard wrote down the sum of squares of two numbers as shown. Unfortunately, some of the digits cannot be seen because they are covered in ink.  What is the last digit of the first number?  So we can write out this formula, writing down what we know and writing down question marks for what we don't. The thing to recognize in this problem is  most of these digits are irrelevant. We can actually erase most of them and get a simplified formula like so. An unknown digit squared plus 2 squared equals 29.  All we did is ignore the digits before since we are only interested in the last digit of the first number. Simplifying this further, we get 2 squared equal to 4.  Now we can subtract 4 from both sides and we get a number to the power of 2 equal to 25. When we do the square root of 25, we will get our answer which will be C, 5.

Video Summary

Question 10. Gerard wrote down the sum of squares of two numbers as shown. Unfortunately, some of the digits cannot be seen because they are covered in ink. What is the last digit of the first number? So we can write out this formula, writing down what we know and writing down question marks for what we don't. The thing to recognize in this problem is most of these digits are irrelevant. We can actually erase most of them and get a simplified formula like so. An unknown digit squared plus 2 squared equals 29. All we did is ignore the digits before since we are only interested in the last digit of the first number. Simplifying this further, we get 2 squared equal to 4. Now we can subtract 4 from both sides and we get a number to the power of 2 equal to 25. When we do the square root of 25, we will get our answer which will be C, 5.

Keywords

sum of squares

last digit

simplified formula

square root

unknown digit