model 4 addition, subtraction, multiplication and division with lcm & hcf Section-Wise Topic Notes With Detailed Explanation And Example Questions

Answer: (b)

LCM of 12, 18 and 21

= 2 × 3 × 2 × 3 × 7 = 252

Of the options, 10080 ÷ 252 = 40

Answer: (d)

Let no. are x and y and HCF = A, LCM = B

Using Rule, we have

xy = AB

⇒ x + y = A + B (given) ...(i)

$(x–y)^2$ = $(x+y)^2$ – 4xy

or, $(x–y)^2$ = $(A+B)^2$ – 4 AB

$(x–y)^2$ = $(A–B)^2$

(x–y) = A – B ...(ii)

Using (i) and (ii), we get

x = A and y = B

∴ $A^3 + B^3 = x^3 + y^3$

Answer: (a)

We find LCM of 30, 36 and 80.

LCM = 2 × 2 × 3 × 3 × 4 × 5 = 720

∴ Required number = 2 × 720 + 11

= 1440 + 11 = 1451