Need help please :)
- Thread starter Molly44
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Otis
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Hi Molly. The chemical concentration is the same in any amount of a specific solution. In other words, any volume of the solution in your exercise must have a concentration equal to 25mg/50mL.
You're trying to find ?mg/10mL. That ratio must equal 25mg/50mL.
?mg/10mL = 25mg/50mL
If we omit the units, then we may write:
?/10 = 25/50
When two fractions are equal, we call it a proportion.
Do you see that 25/50 is the same as 1/2? (If not, then reduce the fraction 25/50, by dividing numerator and denominator each by 25.)
?/10 = 1/2
That's the same as asking, "How many tenths equal 1/2".
0.5 is the decimal form of 1/2. In other words, five tenths equals 1/2.
Therefore, we have 5mg/10mL = 25mg/50mL, and the answer is 5mg.
Another way to solve a proportion (like ?/10=1/2) is to use a two-step Arithmetic rule: Multiply the two numbers on the diagonal, and then divide by the number not used.
The 'diagonal' refers to an imaginary line drawn through the numerator of one fraction and the denominator of the other fraction (or vice versa).
?/10 = 1/2
Here, the diagonal goes through 10 and 1 because we can multiply 10×1. (If we considered the other diagonal, we could not multiply ?×2 because we don't know both numbers.)
After multiplying 10×1, we divide the product by the number not used (which is 2):
(10×1) ÷ 2 = 10/2 = 5.
Another example: Solve the proportion 2/7=4/?
Multiply on the diagonal: 7×4 gives 28
Divide by the number not used: 28÷2 = 14
Therefore, the unknown number is 14, and we have
2/7 = 4/14
And another example: How many mL of H2O need to be mixed with 7mg of salt, to obtain a concentration of 21mg of salt per 36mL of H2O?
7mg/?mL = 21mg/36mL
7/? = 21/36
Multiply on the diagonal: 7×36 is 252
Divide by the number not used: 252÷21 is 12
7mg/12mL = 21mg/36mL
The answer is: 12mL of H2O.
NOTE! If we'd first recognized that 21/36 can be reduced to 7/12 (both 21 and 36 are multiples of 3), then we could have jumped straight to
7/? = 7/12
and the unknown value is obviously 12.
If you'd like help with any of those similar exercises, then please start new threads for new exercises and show us how far you got. Thanks.
?
You're trying to find ?mg/10mL. That ratio must equal 25mg/50mL.
?mg/10mL = 25mg/50mL
If we omit the units, then we may write:
?/10 = 25/50
When two fractions are equal, we call it a proportion.
Do you see that 25/50 is the same as 1/2? (If not, then reduce the fraction 25/50, by dividing numerator and denominator each by 25.)
?/10 = 1/2
That's the same as asking, "How many tenths equal 1/2".
0.5 is the decimal form of 1/2. In other words, five tenths equals 1/2.
Therefore, we have 5mg/10mL = 25mg/50mL, and the answer is 5mg.
Another way to solve a proportion (like ?/10=1/2) is to use a two-step Arithmetic rule: Multiply the two numbers on the diagonal, and then divide by the number not used.
The 'diagonal' refers to an imaginary line drawn through the numerator of one fraction and the denominator of the other fraction (or vice versa).
?/10 = 1/2
Here, the diagonal goes through 10 and 1 because we can multiply 10×1. (If we considered the other diagonal, we could not multiply ?×2 because we don't know both numbers.)
After multiplying 10×1, we divide the product by the number not used (which is 2):
(10×1) ÷ 2 = 10/2 = 5.
Another example: Solve the proportion 2/7=4/?
Multiply on the diagonal: 7×4 gives 28
Divide by the number not used: 28÷2 = 14
Therefore, the unknown number is 14, and we have
2/7 = 4/14
And another example: How many mL of H2O need to be mixed with 7mg of salt, to obtain a concentration of 21mg of salt per 36mL of H2O?
7mg/?mL = 21mg/36mL
7/? = 21/36
Multiply on the diagonal: 7×36 is 252
Divide by the number not used: 252÷21 is 12
7mg/12mL = 21mg/36mL
The answer is: 12mL of H2O.
NOTE! If we'd first recognized that 21/36 can be reduced to 7/12 (both 21 and 36 are multiples of 3), then we could have jumped straight to
7/? = 7/12
and the unknown value is obviously 12.
If you'd like help with any of those similar exercises, then please start new threads for new exercises and show us how far you got. Thanks.
?