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

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

Answer: (b)

Let the numbers be 21x and 21y

where x and y are prime to each other.

21x + 21y = 336

21 (x + y) = 336

x + y = $336/21$ = 16

∴ Possible pairs = (1, 15), (5, 11), (7, 9), (3, 13)

Answer: (b)

Let the numbers be 7x and 7y

where x and y are co-prime.

Now, LCM of 7x and 7y = 7xy

∴ 7xy = 140 ⇒ xy = $140/7$ = 20

Now, required values of x and y whose product is 50 and are coprime, will be 4 and 5.

∴ Numbers are 28 and 35 which lie between 20 and 45.

∴ Required sum = 28 + 35 = 63.

Answer: (b)

LCM of 12, 18 and 21

= 2 × 3 × 2 × 3 × 7 = 252

Of the options, 10080 ÷ 252 = 40

Answer: (d)

Let HCF be h and LCM be l.

Then, l = 84h and l + h = 680

→ 84h + h = 680

→ h = $680/85$ = 8

∴ l = 680 – 8 = 672

∴ Other number = ${672× 8}/56$ = 96