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# [Smart Math] Arithmetic Problem 5

Here’s and example of a SMART MATH problem for ARITHMETIC.

### Problem

If $x*y$ means $y(x-y)$; find the value of 3.124*1.39.

1. 2.41324
2. 3.24026
3. 4.00236
4. 2.41026
5. 2.313456

### The Usual Method

Substituting the values of ‘x’ and ‘y’ according to the data given, we get

$1.39\times (3.124-1.39)$
i.e. $1.39\times 1.734$

= 2.41026

(Ans: 4)

Estimated Time to arrive at the answer = 90 seconds as this is a calculation intensive problem.

### Using Technique

Just get to the ‘$1.39\times 1.734$’ level. Note that the product of these two numbers should be 2+3 = 5 digits after the decimal point. This eliminates option ‘5’.

Also, the product of the last digits is ‘6’ (9 x 4 = 36). Hence, ‘6’ should be the last digit of the answer. This eliminates option ‘1’.

Also, note that 13 x 17 > 200. Hence, the answer should be a number starting with 2.something…