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What is 30 multiplied by 30?
A. 600
B. 900
C. 960
D. 990
Correct Answer Is Option = 900
Notes / Explanation
When the number thirty is multiplied by thirty, the result is nine hundred, and this calculation, which is an example of a number multiplied by itself, provides a good opportunity to reflect on multiplication and on the idea of a square number. When a number is multiplied by itself, the result is called the square of that number, so that nine hundred is the square of thirty, and multiplying thirty by thirty is the same as squaring thirty. Such calculations appear frequently in mathematics, for example in problems involving areas, since the area of a square shape is found by multiplying the length of its side by itself, so that a square with sides of thirty units has an area of nine hundred square units. This particular calculation is quite easy to work out, because it involves round numbers. One simple way to work it out is to note that thirty is three tens, so that thirty multiplied by thirty is the same as three multiplied by three, which is nine, followed by the appropriate number of zeros from the tens, giving nine hundred. Another way to see it is to note that thirty multiplied by thirty can be worked out by first multiplying thirty by three to get ninety, and then multiplying by ten to get nine hundred. Multiplying by numbers that are multiples of ten is made easier by the fact that one can multiply the simple numbers and then account for the zeros. A good command of multiplication, including the multiplication of round numbers and the squaring of numbers, is very useful, both for solving problems in mathematics and for dealing with many practical situations. Knowing the squares of the round numbers, such as ten, twenty, thirty, forty and so on, is particularly useful, since these appear often and are easy to remember, being simply the square of the simple number followed by the appropriate zeros. Questions testing the ability to carry out such calculations are common in examinations. For PPSC and other competitive examinations, the key points to remember are that thirty multiplied by thirty equals nine hundred, that a number multiplied by itself gives its square, so that nine hundred is the square of thirty, that this calculation is made easy by the fact that thirty is a round number, being three tens, so that one can multiply three by three to get nine and then add the zeros, and that knowing the squares of the round numbers is useful because they appear often and are easy to work out.
