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## Using symbols instead of numbers

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**Using symbols instead of numbers**What number can be added to 21 to get 50? + 15 = 27 7 x = 56 Sometimes questions have a missing number that you need to find.**Using symbols instead of numbers**What number can be added to 21 to get 50? 29 22 + 15 = 27 7 x 8 = 56 Sometimes questions have a missing number that you need to find.**Using symbols instead of numbers**We often use a symbol to represent that missing number. Sometimes this is a letter. P + 43 = 80 4 x n = 24**Using symbols instead of numbers**We can use a variety of strategies to solve these: TRIAL & ERROR TRIAL & IMPROVEMENT INVERSES**Using symbols instead of numbers**TRIAL & ERROR – also known as guesswork! This is the most basic method. Guess various numbers and see if they work. It is not very efficient and doesn’t always give you the answer. 26 + w = 94**Using symbols instead of numbers**TRIAL & ERROR – also known as guesswork! This is the most basic method. Guess various numbers and see if they work. It is not very efficient and doesn’t always give you the answer. 26 + w = 94 80?**Using symbols instead of numbers**TRIAL & ERROR – also known as guesswork! This is the most basic method. Guess various numbers and see if they work. It is not very efficient and doesn’t always give you the answer. 26 + w = 94 80? x**Using symbols instead of numbers**TRIAL & ERROR – also known as guesswork! This is the most basic method. Guess various numbers and see if they work. It is not very efficient and doesn’t always give you the answer. 26 + w = 94 70?**Using symbols instead of numbers**TRIAL & ERROR – also known as guesswork! This is the most basic method. Guess various numbers and see if they work. It is not very efficient and doesn’t always give you the answer. 26 + w = 94 70? x**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 80? gives 106 – too big! So lets look at numbers less than 80.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 70? gives 96 – too big! So lets look at numbers less than 70.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 60? gives 86 – too small! So lets look at numbers between 60 and 70.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 65? gives 91 – too small! So lets look at numbers between 65 and 70.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 67? gives 93 – too small! So lets look at numbers between 67 and 70.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 69? gives 95 – too big! So lets look at numbers between 67 and 69.**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 68? Gives 94 – correct!**Using symbols instead of numbers**TRIAL & IMPROVEMENT – educated guesswork that gets more accurate! This method usually gets you to the answer, but can take a long time. It helps if you say if the answer is too big, too small, or correct. 26 + w = 94 w = 68**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. 26 + w = 94 The INVERSE of + is -**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. w = 94 - 26 The INVERSE of + is -**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. w = 68 The INVERSE of + is -**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. d x 9 = 54 The inverse of x is ÷**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. d = 54 ÷ 9 The inverse of x is ÷**Using symbols instead of numbers**INVERSES – using the “undo” method. This method will always get you the answer, and will often be the quickest method. It is, however, slightly trickier. d = 6 The inverse of x is ÷**Using symbols instead of numbers**Try these: 6 + a = 19 b + 43 = 60 15 – c = 2 Be careful with these ones d – 26 = 90 e x 4 = 32 7 x f = 77 g ÷ 10 = 120 300 ÷ h = 6**Using symbols instead of numbers**Try these: 6 + a = 19 a = b + 43 = 60 b = 15 – c = 2 c = d – 26 = 90 d = e x 4 = 32 e = 7 x f = 77 f = g ÷ 10 = 120 g = 300 ÷ h = 6 h =**Using symbols instead of numbers**Try these: 6 + a = 19 a = 19 - 6 b + 43 = 60 b = 60 – 43 15 – c = 2 c = 15 - 2 d – 26 = 90 d = 90 + 26 e x 4 = 32 e = 32 ÷ 4 7 x f = 77 f = 77 ÷ 7 g ÷ 10 = 120 g = 120 x 10 300 ÷ h = 6 h = 300 ÷ 6**Using symbols instead of numbers**Try these: 6 + a = 19 a = 13 b + 43 = 60 b = 17 15 – c = 2 c = 13 d – 26 = 90 d = 116 e x 4 = 32 e = 8 7 x f = 77 f = 11 g ÷ 10 = 120 g = 1200 300 ÷ h = 6 h = 50