9/20-12/17

Let's evaluate: $\frac{9}{20}-\frac{12}{17}$

ⓘ To add fractions, put them over the same denominator, then add the numerators. We choose $340$, the least common multiple of $20$ and $17$. Multiplying the numerator and the denominator by the same number does not change the fraction: $\frac{9}{20}-\frac{12}{17}$ = $\frac{9\times 17}{20\times 17}-\frac{12\times 20}{17\times 20}$ = $\frac{9\times 17-12\times 20}{20\times 17}$

$\frac{9\times 17-12\times 20}{20\times 17}$

ⓘ Perform multiplications before additions and subtractions: $9\times 17$ = $9\times (10+7)$ = $9\times 10+9\times 7$ = $90+63$ = $153$, $12\times 20$ = $(10+2)\times 20$ = $10\times 20+2\times 20$ = $200+40$ = $240$

ⅰ $20\times 17$ = $20\times (10+7)$ = $20\times 10+20\times 7$ = $200+140$ = $340$

$\frac{153-240}{340}$

ⓘ Calculate the numerator and denominator before dividing: $153-240$ = $-87$

▶Result:   $-\frac{87}{340}$

The numeric value of: $-\frac{87}{340}$ equals:

▷ $\approx -0.2559$