MGMAT Flashcards
Unknown Digits Problems
- Be ready to create variables to represent unknown digits.
- Recognize that each unknown is restricted to at most ten possible values (0-9).
- Apply any given constraints, may involve number properties like divisibility or odds & evens.
Powers of 10 & Decimals
- When you multiply by a power of 10, move the decimal right the number of specified places.
- When you divide by a power of 10, move the decimal left.
- Negative powers of 10 reverse the process.
“trading decimal places for powers of ten”
How to find the Last Digit Shortcut
- Drop any digits but the ones unit from all numbers.
- Multiply/add all the ones digits.
- Take the ones digit of the final product.
Why use Heavy Division Shortcut
To solve division problems with complex decimals:
How to use Heavy Division Shortcut
- Set up the division problem in fraction form.
- Rewrite the problem, eliminating powers of 10.
- Get a single digit to the left of the decimal in the denominator.
- Focus on the whole number parts of the numerator and denominator and solve.
- if not precise enough, keep one more decimal place and do long division.
What do you do with the decimal in Addition Subraction
- make sure to line up the decimal points and make decimals the same length.
What do you do with the decimal in Multiplication:
- ignore the decimal until the end.
- multiply and count the total number of digits to the right of the decimal in both factors. Put that many digits in the product.
- if multiplying a very small and large number, move decimals in the opposite direction to make the same number of places.
What do you do with the decimal in Division
- if a decimal In the dividend (inner #), bring the decimal point straight up to the answer and divide.
- if a decimal in the divisor (outer #), shift the decimal point in both the divisor and dividend to make the divisor a whole number. Then divide.
- simplify division by moving decimals in the same direction.
How do you take a power or a root of a decimal
By splitting the decimal into 2 parts: an integer and a power of ten.
the number of decimal places in a cube is HOW MANY TIMES the number of decimals in the original number.
the number of decimal places in a cube is 3x the number of decimals in the original number.
- the number of decimals in a cube root is WHAT FRACTION of the number in the original.
- the number of decimals in a cube root is 1/3 the number in the original.
What are proper fractions
are those that fall between 0 and 1, numerator always smaller than denominator.
What are improper fractions
greater than 1, numerator greater than denominator.
What are mixed numbers
Mixed numbers: written as integer and proper fraction.
What are Complex Fractions
sum or difference in numerator/denominator
For positive fractions,
1. As the numerator increases,
the fraction increases.
For positive fractions,2. As the denominator increases,
the fraction decreases.
For positive fractions,Adding the same number to both the numerator and denominator brings the fraction
closer to 1.
What is The Multiplication Shortcut
Before multiplying fractions, cancel out factors to reduce to simpler numbers.
Adding, subtracting, multiplying, and dividing each fraction each respectively does what
Adding - increases the value
Subtracting - decreases the value
Multiplying - decreases the value
Dividing - increases the value
How to compare fractions
- Set the fractions next to each other.
- Cross multiply the fractions and put each answer by the corresponding numerator.
- Compare the answers.
What is the shortcut for addition and subracton of fractions
There is no shortcut
What must you do to add or subtract fractions
1) Find a common denominator
2) Change each fractioon so that it is expressed using this common denominator
3) add up the numerators only
What must you do to divide fractions
Flip the second fraction and multiply
What do do with DOUBLE DECKER fractions ie (1/2) / (3/4)
= 1/2 * 4/3
When simplifying fractions, that incorporate fractions, what must you remember about the numerator and denominator
You may may split the numerator but you may NEVER split the denominator
100% = what number
1
Percents can be converted into decimals by
moving the decimal point 2 spaces to the left
Remember, the percentage is always WHAT than the decimal
BIGGER
How to write A PART is some PERCENT of a WHOLE
A PART is some PERCENT of a WHOLE
How to find 10% of any number
Just move the decimal point to the left one place
Increasing - percent of original
If a quantity is increasing by x%, the the new quantity is (100+x)% OF the original.
decreasing -percent of original
If a quantity is decreasing by x%, then the new quantity is (100-x)% OF the original.
ORIGINAL x (1 + [percent increase/100] ORIGINAL x (1 + [percent increase/100] = WHAT
NEW
Original + Change = WHAT
Percent Change
What is so tricky about Successive percents
They cannot simply be added or subtracted together.
They cannot simply be added or subtracted together.
How to solve successive percents
Choose real numbers and see what happens: 100 is the easiest number to choose.
ORIGINAL x (1+x%) x (1+y%) = FINAL
Simple interest
principal x rate x time
Compound Interest
P = C (1 + r/n) nt
where
P = future value
C = initial deposit
r = interest rate (expressed as a fraction: eg. 0.06)
n = # of times per year interest is compounded
t = number of years invested
What should be set up with chemical mixture problems
set up a mixture chart with the substance labels in rows and “original” “change” and “new” in the colums. This way, you can keep careful track of the vatious components and their changes.
1/100 0.01 1% 1/50 0.02 2% 1/25 0.04 4% 1/20 0.05 5% 1/10 0.10 10% 1/9 0.11(repeat) 11.1% 1/8 0.125 12.5% 1/6 0.16(6 repeat) 16.7% 1/5 0.2 20% 1/4 0.25 25% 3/10 0.3 30% 1/3 0.3(repeat) 33% 3/8 0.375 37.5% 2/5 0.4 40% 1/2 0.5 50% 3/5 0.6 60% 5/8 0.625 62.5% 2/3 0.6(repeat) 66.6% 7/10 0.7 70% 3/4 0.75 75% 4/5 0.8 80% 5/6 0.83(3 repeat) 83.3% 7/8 0.875 87.5% 9/10 0.9 90% 1/1 1 or 100% 5/4 1.25 125% 4/3 1.3(3 repeat) 133% 3/2 1.5 150% 7/4 1.75 175%
MEMORIZE
When to use?
Fractions:
- canceling factors in multiplication
- best way to exactly express proportions
When to use?
- estimate results or compare sizes
Prefer fractions for doing what 2 things
multiplication or division;
prefer decimals and Percents for what 4 things
doing addition and subtraction, for estimating numbers, or for comparing numbers.