How to find the whole from the part - ISEE Middle Level Quantitative Reasoning

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Question

150% of what number is 9,000?

Answer

Taking 150% of a number is the same as multiplying that number by 1.5. We can find our number, therefore, by dividing 9,000 by 1.5:

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Question

is a multiple of 2, but not a multiple of 6. If is divided by 6, What could be the remainder?

Answer

If the remainder of dividing by 6 is 0, then must be a multiple of 6, which contradicts what we are given.

Suppose we call and the quotient and remainder, respectively, of dividing by 6. Then

If the remainder is 1, then

, as a product of two integers, one even, is an even number; if 1 is added, the result is odd. Therefore, if 1 is the remainder, is odd, which also contradicts what we are given about . 1 cannot be the remainder, and for similar reasons, neither can 3.

This leaves 2, which can be the remainder; for example, 8, which is a multiple of 2, but not a multiple of 6, yields a quotient of 1 and a remainder of 2 when divided by 2.

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Question

After a discount of 20%, a boom box costs $144.

Which is the greater quantity?

(a) The price of the boom box before the discount

(b) $172.80

Answer

Paying for something at 20% discount is the same as paying for it at 80% of the price.

If the boom box costs $172.80 before a 20% discount, then afterward, it costs 80% of this, or

Therefore, the original price must have been greater than $172.80.

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Question

40% of is 200

70% of is 350

Which is the greater quantity?

(a)

(b)

Answer

Each statement can be written as a proportion, and solved for its variable by cross-multiplying. In each case, we replace as follows:

(a) The percent is 40, the part is 200, and the whole is :

(b) The percent is 70, the part is 350, and the whole is :

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Question

Chet bought an MP3 player and got $14.50 back in change. The tax on the MP3 player was 5%.

Which is the greater quantity?

(a) The price of the MP3 player before tax

(b)

Answer

No clue is given as to how much Chet paid for the device - neither the price paid for the player nor the amount of money Chet gave the clerk is given here.

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Question

60% of 3,000 is equal to 40% of what number?

Answer

60% of 3,000 is equal to .

40% of an unknown number can be written as . Set these equal and solve for :

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Question

Claude bought a new game for $32 at 20% off its original price. What was the original price of the game?

Answer

Since the game was 20% off, that means the game's value is currently 80% of the original price.

In order to figure out what the original price of the game was, you must set up a proportion:

The proportion is set up this way because the $32 Claude paid is equal to 80% of the price of the game, not 100%. The x stands for the unknown original price of the game. Next, cross multiply. The bottom number of each fraction should be multiplied by the top number.

The above will be your result. You then must solve for x. To do this, divide by 80 on each side of the equation.

The value of x is your answer.

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Question

is % of what number?

Round to the nearest thousandth.

Answer

Remember that for percentages, the key to setting up the problem is intelligent translation. The word "is" becomes , "of" signals multiplication, "what" (and equivalent words) signal a variable ().

Therefore, we can translate:

is % of what number?

As...

To solve, divide both sides by :

Rounded, this is:

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Question

is % of what number?

Round to the nearest thousandth.

Answer

Remember that for percentages, the key to setting up the problem is intelligent translation. The word "is" becomes , "of" signals multiplication, "what" (and equivalent words) signal a variable ().

Therefore, we can translate:

is % of what number?

As . . .

To solve, divide both sides by :

Rounded, this is:

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Question

is % of what number?

Round to the nearest thousandth.

Answer

Remember that for percentages, the key to setting up the problem is intelligent translation. The word "is" becomes , "of" signals multiplication, "what" (and equivalent words) signal a variable ().

Therefore, we can translate:

is % of what number?

As...

To solve, divide both sides by :

Rounded, this is:

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Question

500 is of what number?

Answer

of a number is equal to

of the number.

The question becomes equivalent to asking this - 500 is of what number?

We can find out by dividing 500 by :

.

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