Solve 21div{(7-15)3+[9-(18+3)div4]}=

$$21 \div \{ ( 7 - 15 ) 3 + [ 9 - ( 18 + 3 ) \div 4 ] \} =$$

Evaluate

$$-\frac{28}{27}\approx -1.037037037$$

Solution Steps

Subtract 15 from 7 to get -8.

$$\frac{21}{-8\times 3+9-\frac{18+3}{4}}$$

Multiply -8 and 3 to get -24.

$$\frac{21}{-24+9-\frac{18+3}{4}}$$

Add -24 and 9 to get -15.

$$\frac{21}{-15-\frac{18+3}{4}}$$

Add 18 and 3 to get 21.

$$\frac{21}{-15-\frac{21}{4}}$$

Convert -15 to fraction -\frac{60}{4}.

$$\frac{21}{-\frac{60}{4}-\frac{21}{4}}$$

Since -\frac{60}{4} and \frac{21}{4} have the same denominator, subtract them by subtracting their numerators.

$$\frac{21}{\frac{-60-21}{4}}$$

Subtract 21 from -60 to get -81.

$$\frac{21}{-\frac{81}{4}}$$

Divide 21 by -\frac{81}{4} by multiplying 21 by the reciprocal of -\frac{81}{4}.

$$21\left(-\frac{4}{81}\right)$$

Express 21\left(-\frac{4}{81}\right) as a single fraction.

$$\frac{21\left(-4\right)}{81}$$

Multiply 21 and -4 to get -84.

$$\frac{-84}{81}$$

Reduce the fraction \frac{-84}{81} to lowest terms by extracting and canceling out 3.

$$-\frac{28}{27}$$

Factor

$$-\frac{28}{27} = -1\frac{1}{27} = -1.037037037037037$$