MCQ
Find $81.4 \times 80.3$ using a suitable identity.
- A$6434.42$
- B$6536.036$
- C$653.642$
- ✓$6536.42$
✓
Answer
Correct option: D.
$6536.42$
D. $6536.42$
Solution:
$81.4 \times 80.3=(80+1.4) \times(80+0.3)$
Using identity $(x+a)(x+b)=x^2+(a+b) x+a b$
$(80+1.4) \times(80+0.3)=(80)^2+(1.4+0.3) \times 80+1.4 \times 0.3=6400+1.7 \times 80+0.42$
$=\ 6400+136+0.42$
$=\ 6536.42$
Solution:
$81.4 \times 80.3=(80+1.4) \times(80+0.3)$
Using identity $(x+a)(x+b)=x^2+(a+b) x+a b$
$(80+1.4) \times(80+0.3)=(80)^2+(1.4+0.3) \times 80+1.4 \times 0.3=6400+1.7 \times 80+0.42$
$=\ 6400+136+0.42$
$=\ 6536.42$
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